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Woolly Bear

Personally, I haven’t seen very many woolly bears this fall but a lot of people visiting the nursery lately have and they say that these fat, furry caterpillars are mostly black this year. “What does that mean about the coming winter?”, they often ask. It’s hard for people to remember how this little tale goes.

So, in honor of Halloween and the imminent end of Daylight Savings, I thought I’d re-post my woolly bear story.

Here you go – from September 2010 …

Can woolly bears really predict the weather?

Do woolly bears really predict the weather?

They’re beginning to cross the road in front of my car as I drive to work in the morning – everyday I see more of them. It has gotten me thinking about these beloved fuzzy caterpillars that children of ALL ages find irresistible. You have to admit – they really are pretty cute!

Most of us have heard the story about how woolly bears can predict the severity of the coming winter by the pattern of the orange and black stripes on their fuzzy bodies . . .
but is there any truth in the tale? And how does the story go – does a wide orange band mean a harder winter or is it a narrow orange band and lots of black that predicts the hard winter? I, for one, can never remember!

Well here’s the scoop straight from the Old Farmer’s Almanac:

The longer the middle orange band on the woolly bear, the milder and shorter the winter will be. Conversely, the shorter the orange band, hence the more black on the woolly bear, the longer and harsher the winter will be.

This woolly bear would predict a short, mild winter. Boy was he off on his prediction!

This woolly bear would predict a short, mild
winter. Boy was he off on his prediction!

Now, is there any scientific evidence to back this bit of folklore? In a word – no!

Well, I mean not really. The lengths of the orange and black bands are really a function of the age of the caterpillar. Woolly bears are the larval stage of the Isabella Tiger Moth, a not-very-impressive moth that you might see fluttering around your porch lights at night during the summer. The woolly bear caterpillars molt (shed their skin) several times as they grow and each time they do, the orange band gets longer and the black ends get shorter. So if you see a woolly bear that is mostly orange, that just means it’s older and more mature!

So much for their prediction of the winter of 2009-2010! Our woolly  bears were way off last year!

So much for their prediction of
the winter of 2009-2010! Our woolly
bears were way off last year!

But here’s some food for thought … what if you have a long, mild fall? The woolly bears will stay active longer and keep growing and molting. The orange band will become wider and wider! Hmmmm, does a mild fall predict a mild winter? And what if winter comes early? A shorter fall season will mean that the woolly bears are younger/haven’t molted as often before they seek shelter for the winter, resulting in a relatively narrow orange band and more black on their fuzzy bodies. Is a harsh winter on the way?

The woolly bears I found around the nursery last year were an epic failure as far as predicting our winter – most had a lot of orange and very little black! A mild winter? Not by a long shot! We had one of the hardest, snowiest winters on record in the Shenandoah Valley!

I wonder if they’ll do any better this year. I haven’t seen any close enough yet to see their color pattern – have you?

Happy Halloween everybody!

Native dogwoods have beautiful fall color

The trees are donning their brilliant fall colors, the fields of corn and soybeans are being harvested, the last tomatoes and beans are being picked from the garden – fall is here!

pruning with hand shearsThese beautiful, crisp, cool days of autumn are when we begin to put our gardens to bed for the season. This has many gardeners venturing out with shears in hand to primp and prune and otherwise tidy up in the garden.
While it is a great idea to cut back some of your herbaceous perennials in the fall, you should keep your pruning shears and loppers away from your trees and shrubs for a while yet.

Why? Because pruning stimulates regrowth. Plants respond to pruning with a burst of new growth; the more severe the pruning, the heavier the regrowth. If this growth occurs during the warm days of fall, the tender new shoots that develop will not have time to harden before the winter cold sets in and they become prone to winter damage.

A majestic oak silhouetted against the winter sky

A majestic oak silhouetted
against the winter sky

In general, woody plants should be pruned when they are dormant. This usually means in late fall, winter, or early spring.

How do you know when trees and shrubs are dormant?

It’s easy enough to tell when deciduous trees and shrubs are dormant because they lose their leaves but it’s not as clear cut with evergreens since they keep their leaves through the winter. Luckily, evergreen trees and shrubs normally enter dormancy in the late fall around the same time as deciduous plants.

Not all pruning is done during the dormant period

Pruning quince at the wrong time leads to loss of bloom

Pruning flowering quince at the wrong
time leads to loss of the bloom

Though trees and shrubs can always be pruned when they are dormant, there are good reasons to delay pruning of some species. This is especially true when it comes to the spring flowering trees and shrubs. If you prune these during the dormant period, you will be removing many if not all of the flower buds and this will obviously impact the spring bloom!

Many gardeners are tempted to prune their trees and shrubs in the fall as part of their fall clean-up chores – to tidy up scraggly looking or overgrown plants. Before you cut (even if they are dormant), it is important to think about when they flower and the age of the wood that produces the flowers.

Spring blooming shrubs like rhododendron should be pruned after flowering

Spring blooming shrubs like
rhododendron should be pruned
right after they finish flowering

Generally, trees and shrubs that flower in the spring form their flower buds in the previous season, usually in the late summer or early fall. These plants flower on “old wood” or growth that was produced the summer before. Because the flower buds are already set on the branches, you should try to avoid pruning them in the fall, winter, or spring. Shrubs like azalea, rhododendron, lilac, some hydrangea, forsythia, viburnum, and trees like dogwood, redbud, and crabapple fall into this category.

The best time to prune these spring bloomers is right after they finish blooming. Pruning at this time can range from simple deadheading of spent blooms to heading back branches and thinning to reshape or reduce the size of the plant. Here are some tips for pruning spring blooming shrubs.

American holly tree after severe pruning

American holly after severe pruning

The exception to this rule is if you want to do any heavy pruning. Severe pruning, including rejuvenation pruning where you might cut a shrub down to 12″ to 24″ or lower, should be done when the plant is dormant – usually in March. Obviously you must sacrifice the bloom for that season and possibly the following season as well but in most cases, you will be rewarded with a beautiful “new” shrub. Not all shrubs can be pruned hard like this so be sure to do some research before you start chopping!

Summer flowering trees and shrubs form flower buds on the new growth that is produced in the spring and summer. These are normally pruned in the spring before growth begins. However in colder regions, we often recommend that you delay pruning until the threat of very cold weather is past. This sometimes means pruning after growth has begun but don’t worry, it won’t hurt the plant.

Summer pruning

Summer is a good time to prune certain trees and shrubs if you don’t want to encourage a lot of new growth. As I mentioned earlier, pruning stimulates growth, especially when it is done in the spring. Pruning in summer has a dwarfing effect because growth is slower at this time.

This Kieffer pear was pruned in winter. This resulted in vigorous water sprout growth.

This Kieffer pear was pruned in winter.
This resulted in vigorous water sprout
growth in the spring.

For instance, summer is a great time to prune water sprouts – those vigorous stems that grow straight up parallel to the main stem. Pruning them out in the summer can reduce the number of water sprouts that will develop the following season.

Summer is also a good time to prune trees that are heavy bleeders like maple, birch, and dogwood. It is best to avoid pruning these trees just before and during active growth in the spring because they have a heavy sap flow at this time.

A good pruning book will give you recommendations on the timing and techniques for pruning specific trees and shrubs. A handbook like this is a valuable addition to your gardening library.

For more pruning tips, visit our website.

Until next time – Happy Gardening!

Hydrangea macrophylla is blue when grown in acidic soil

Recently, several questions related to pruning different trees and shrubs have come to my inbox or have been posted to our Discussion Board. One of these questions was regarding Endless Summer hydrangea.

I have 7 Endless Summer Hydrangeas that did not bloom at all this year. In previous years, I had tons of blooms, so I did something wrong when I pruned them. I can’t remember what time of year it was the last time I pruned them, but I have not touched them at all this year. They are lush and green and growing, but no flowers. When should I prune them to ensure flowers next spring and summer? I live in Southern NH, about 50 miles north of Boston.”

Lacecaps are beautiful in summer as long as the flower buds survive the winter.

Lacecaps are beautiful as long as
the flower buds survive the winter.

Hydrangea macrophylla, which includes the mophead and lacecap hydrangeas, normally blooms on “old wood”; that is, growth that was produced in the previous season. At the northern edge of their hardiness range, the flower buds of these hydrangeas, which are formed in August and September, are sometimes damaged or killed during severe winters. This means few or no blooms the following season. This happened to my lacecaps this year. In addition, if these shrubs are pruned at the wrong time (in the fall or spring), all those flower buds will be removed and oops – again, no flowers!

The Endless Summer Series is a unique group of Hydrangea macrophylla that blooms on both old wood and new wood. How cool is that? They are also hardier than lacecaps and other mopheads, surviving and blooming even as far north as Zone 4!

Endless Summer flowers are pink in less acidic soils

Endless Summer flowers are pink
in soils that have a higher pH.

If the flower buds that are produced in the fall are killed during a severe winter, no problem! These Endless Summer hydrangeas will still bloom later in the summer, since they readily produce flower buds on the current season’s growth. Because of this trait, they normally flower reliably every year regardless of winter severity.

Then what is happening with these seven Endless Summer hydrangeas?
Why didn’t they bloom?

That’s a good question but I suspect that it is not an issue of improper pruning. Regardless of how you prune these shrubs (unless you keep whacking back the new growth all summer), you should still get at least some summer blooms as long as they are healthy, get enough sun, and are fed and watered properly.

Beautiful, healthy green growth but no flowers.

Beautiful, healthy green growth
but no flowers.

The problem here is more likely to be related to nutrition. Since these shrubs have lush leafy growth, it seems that they are healthy and growing well – perhaps too well. If a flowering plant receives too much nitrogen, it will grow like gangbusters and “forget about” producing flowers. This is what you want for your grass – not your flowering plants.

In fact, this is sometimes what happens when flowering trees and shrubs are planted in the lawn rather than in designated flowerbeds. Your lawn is fertilized with a high nitrogen fertilizer so it grows lush and green but guess what? If your flowering plants are growing in the lawn, they are getting the same high nitrogen food. What’s their response? Grow lots of foliage and no flowers! The nutrient responsible for flower bud production is phosphorus, an element that has recently been removed from most lawn fertilizers.

I have no idea if this is the situation for these particular Endless Summer hydrangeas, but regardless of where they are growing, these shrubs may just need a shot of phosphorus in order to initiate flower bud production. A bloom booster fertilizer or Espoma Triple Super Phosphate (0-45-0) might do the trick. I suggested that she feed them with a good quality organic fertilizer such as Espoma Holly-tone plus an application of Super Phosphate according to the label directions. Hopefully, this will help and her Endless Summer hydrangeas will bloom next season.

So what about pruning?

How and when DO you prune Endless Summer hydrangeas?
The best time to do any structural pruning is just after they finish their initial bloom in early summer.

Dead stems should be cut back to live wood with healthy buds.

Dead stems should be cut back to
live green wood with healthy buds.

In the spring once the new leaves have fully expanded, any branch tips that were killed over the winter should be pruned back to live wood. In more northern areas, this may mean more extensive pruning and the loss of the early bloom.

When the first blooms fade, do any necessary pruning to reshape or reduce their size or just deadhead the flowers. This pruning will stimulate new growth and the formation of flower buds for the summer rebloom. Deadhead the flowers throughout the summer to encourage the production of additional blooms. You can even cut flowering stems for indoor arrangements and this will stimulate the production of more flowers!

All pruning of Hydrangea macrophylla, including the Endless Summer varieties,  should be completed by the end of July because after that, in August and September, the flower buds for the next season’s early bloom will be forming.

Until next time – Happy Gardening!

Here They Come in Droves!

Boxelder bug nymphs

Aaaagh! They’re swarming all over the house! It’s like a scene from an Alfred Hitchcock horror movie! There are masses of them crawling over every screen trying to get in! Many can guess what I’m talking about – STINK BUGS!

Brown marmorated stink bug

Brown marmorated stink bug

The brown marmorated stink bug (Halyomorpha halys) has not only become an annoying invader of our homes but their populations have exploded to the point that they have become a major threat to many agricultural crops including both ornamentals and food crops.

Native to Asia, the brown marmorated stink bug (BMSB) is a relative newcomer to the US being first reported in Pennsylvania in 1998. Since then their numbers and range have slowly increased and they are now found in 30 different US states and are still on the move.

At least, these annoying pests do not bite, sting, suck your blood, or carry diseases that can be transmitted to humans. Thank goodness for small favors!

Stink bugs crawl over the screen

Stink bugs crawl over the screen

Late September and October is the time of year that these nasty pests begin congregating around the windows and doors of our homes seeking a warm place to spend the winter. As I sit here writing this, there is a stink bug flying around our office; crashing into light fixtures, walls, windows…

The sunny weather and unseasonably warm temperatures last Sunday must have rousted them out of their hiding places and encouraged them to start looking for an overwintering site. They were on every window and every door; trying to find any crack or entryway into the cozy, comfort of our house.

In the past few years, we’ve seen a few stink bugs around our house in the fall but never the masses that appeared on Sunday! It was impressive – in a BAD way! It was hard to open the sliding screen door to get to the deck without letting one or two in. Ugh! They were quite determined.

We managed to keep them out mostly. The ones did manage to sneak in provided amusement for the cats for a while until we were able to catch them and toss them out again.

Green stink bugs are also very damaging to vegetable crops.

Green stink bugs are also very
damaging to vegetable crops.

Because this particular species of stink bug is having such an impact on fruit and vegetable crops, a lot of research is being directed towards developing control methods. Some of this research has focused on natural enemies and pheromone traps in addition to chemical controls.

Horned squash bugs, closely related to stink bugs,  swarm on a cucumber vine.

Horned squash bugs, closely related to
stink bugs, swarm on a cucumber vine.

For the time being, exclusion is one of the best preventative measures for controlling populations indoors. Carefully examine the foundation and around windows and doors for cracks and crevices where they can sneak into the house. They will seek out these entry points in an attempt to find overwintering sites. Use caulk and weather stripping to seal any cracks.

 

Luckily our house is fairly tight and unless they sneak in through an open door, few manage to get in. The attic is a different story. I think they can manage to get in up there fairly easily but it’s hard for them to make their way into the rest of the house from the attic.

Boxelder bug nymphs swarm over a statue in the garden

Boxelder bug nymphs swarm over
a statue in the garden

The boxelder bug is another nuisance insect that can invade your home in droves at this time of the year. Like the stink bugs, they are seeking protected overwintering sites and your warm home fits the bill perfectly! I’ve seen swarms of the bright red immature boxelder bugs crawling over concrete statues and the surrounding plants in the Viette gardens at this time of year. I guess the concrete warms up in the sun and they take advantage of this late season warmth the same as they do when they are swarming on the foundation of your house. Creepy!

 

There are several control products available that will kill stink bugs and boxelder bugs on contact. Bonide Household Insect Control kills on contact but also has some residual action that creates a relatively effective barrier around windows, doors, and other areas where these pests might gain entrance to your home. Use according to the label directions.

Brown marmorated stink bug

Stink bugs are super annoying
in the house!

Stink bug traps have also been developed. Some of these traps, like the Bonide Stink Bug Trap and the Rescue Reusable Stink Bug Trap, use pheromones to attract and trap the bugs. The pheromone traps work best in the spring and summer when the stink bugs are seeking mates. Once daytime temperatures drop below 60° in the fall, they don’t work well. At this point, the mating season is over and their attention is focused on finding a place to spend the winter rather than finding a mate.

Traps that use light as an attractant may work better in the fall. The Rescue Stink Bug Trap has an optional light attachment that can be used to attract and trap the stink bugs that have made their way into your home.

I’ve never tried any of these traps but if you have large numbers of stink bugs in your home, they might be worth a try!

If you search online, you can also find other “creative” ways to control stink bugs in your home. Andre prefers the vacuum cleaner but you’d better change the bag afterward!

Until next time – Happy Gardening!

Blue-winged wasp feeds on a clover flower

I had two different inquiries about this particular wasp last week.

Our nursery field manager, “Bo” asked me about them because he had noticed small groups of black wasps flying low over his lawn when he was mowing.

Just the day before, someone happened to e-mail us a photo of one of the wasps that had been hovering over his lawn. When I showed the picture to Bo, he said, “Yes! That’s exactly what they look like!”

Who are they?

Bo said these particular wasps weren’t aggressive at all. They were just flying low over the grass like they were looking for something. Well, that’s exactly what they were doing – looking for beetle grubs.

A blue-winged wasp feeds on the nectar of a clover flower.

A blue-winged wasp feeds on the nectar
of a clover flower. Photo sent in by Ralph.

These are one of the scoliid wasps; a group of fairly large solitary wasps that lay their eggs on the beetle larvae that feed on and damage the roots of your grass.

This particular wasp is the blue-winged wasp, Scolia dubia. It is fairly common throughout the United States. Finding these guys hovering over your lawn is both a good thing and a bad thing. The bad news is that if you see a lot of them, it means that you probably have a healthy population of white grubs in your lawn. The good news is that these wasps are out to parasitize the grubs and can actually help control them in you lawn.

You see, the female wasps search out these grubs and lay their eggs on them – one egg per grub. They dig into the ground under the grass or follow the tunnels made by the grubs. When they locate a grub, they sting it to paralyze it and then lay a single egg on its body. When the egg hatches, the wasp larva feeds on the grub, eventually killing it. Good wasp!

Female scoliid wasps will lay up to two eggs per day over about a two month period. That translates to a lot of dead grubs. The adults are active from June to October but the peak of their breeding activity seems to be in the mid to late summer, which, not coincidentally, corresponds to the hatch of their preferred hosts; green June beetle and Japanese beetle grubs.

Adult wasp visits a Rudbeckia flower

An adult wasp visits a Rudbeckia flower.
Felix Francis, University of Delaware,
Bugwood.org

As an added benefit, the adult wasps feed on the nectar of many different flowers and so aid in pollination. They aren’t the most important pollinators around but in these days of dwindling bee populations, every little bit helps.

All-in-all, these are pretty useful wasps to have around. They usually won’t sting you unless you happen to be a grub and they can help you by killing some of those damaging white grubs in your lawn. Good biological control without chemicals! In fact, these beneficial wasps have sometimes been brought in and released in areas that have severe grub infestations.

Another beneficial solitary “bee”! Who knew there were so many!

Until next time – Happy Gardening!

Deep crack on the bottom of a large tomato. Black mold is beginning to grow in the crack.

It’s been a tough year for tomatoes.

The weather, at least in our area of the Shenandoah Valley, has been cooler than normal and fairly dry. The rain we’ve had has mostly come as heavy downpours – “frog stranglers” as my old boss used to say. We haven’t had many nice steady, soaking rains. Heavy rains, which are often associated with thunderstorms, are usually more destructive than helpful because most of the water runs off without soaking in and takes a lot of topsoil with it.

I saw on the news the other night that so far this summer, we’ve only had 15 days over 90° – the normal is 25 days by this point. Many days in July and August were in the 70’s and nights were often cool – in the 50’s and even several nights when the temperatures dipped into the mid to upper 40’s. Crazy! Nice for us but it has caused some issues in the vegetable garden.

Tomatoes don’t do well in cool weather – especially when the nights are cool. Temperature extremes (daytime temps above 90° or nighttime temps below 55°) cause poor fruit set.

First tomato harvest - 'Pruden's Purple' on July 6th and a nice big pepper, too.

First tomato harvest – ‘Pruden’s Purple’
on July 6th and a nice big pepper, too.

Our tomatoes started the season growing well; producing loads of flowers and setting lots of fruit. We have noticed that after this initial burst in June, everything slowed way down in July and August. We noticed fewer flowers and didn’t see many young tomatoes forming. The tomatoes that formed in June continued to grow and eventually ripened but production has certainly tapered off. I have heard the same complaint from other gardeners. This summer just hasn’t been favorable for growing tomatoes.

I have noticed several different problems on our tomato fruit this year but most of these are issues that I have seen in other years as well. They are fairly common tomato problems.

Growth cracks

These shallow growth cracks have healed over

Shallow growth cracks can heal.

Growth cracks develop in tomatoes when they undergo a spurt of rapid growth during ripening. This often occurs when extended dry conditions are followed by sudden heavy rain or irrigation. This isn’t an unusual situation and has occurred several times in our garden this season. As a result, many of our ripe tomatoes are showing varying degrees of cracking. Growth cracks frequently appear on the top of the tomato near the stem but sometimes when a tomato is fully ripe or overripe, cracks will develop on the bottom of the fruit. Shallow cracks will normally heal over but deeper cracks that develop can become easy pathways for disease and insects to enter and cause secondary problems.

Try to keep your garden soil evenly moist. Mulching definitely helps with this.

Anthracnose

Anthracnose lesion showing concentric rings of fungal fruiting bodies

Anthracnose lesion showing concentric
rings of fungal fruiting bodies

Anthracnose of tomatoes is a disease caused by the fungus Colletotrichum coccodes. It appears as sunken, circular lesions on ripe tomatoes. Often these lesions have concentric rings of black fruiting bodies in the center. Green tomatoes can become infected with anthracnose but the symptoms do not appear until the tomato ripens.

The fungal spores are found in the soil and on plant debris left in the garden. Tomatoes are infected when soil containing spores is splashed up onto the fruit and foliage.

Anthracnose has destroyed half of this tomato

Anthracnose has damaged half
of this tomato

Anthracnose does little damage to the leaves but can cause major damage to mature, ripe tomatoes. This disease is more common during warm, wet weather but spores can also be transmitted to the plants from splashing during overhead irrigation.

Mulching around your tomato plants and trellising or staking them to keep them off the ground will help to prevent this fungal disease. Avoid working among the plants when they are wet and harvest the tomatoes as they ripen and use them promptly.

Infected fruit should be removed to prevent the spread of the disease. Crop rotation and careful clean up of all plant debris in the fall is important for controlling anthracnose.

Cat facing

Cat facing on a large heirloom tomato

Cat facing on a large heirloom tomato

Ever find tomatoes that have funky-shaped, puckered bottoms? This is called cat facing and it is thought to result from the abnormal development of the flower bud or flower – before the fruit is even formed! The factors that lead to cat facing in tomatoes are normally environmental, including cool temperatures before and during flower formation. Hmmmm, that sounds familiar!

Other causes of cat facing in tomatoes are any type of physical damage to the flowers, herbicide damage (such as drift from nearby 2,4-D spraying), and sometimes excessive pruning of tomato plants.

Mild cat facing

Sometimes it isn’t too bad

.

Varieties that produce large tomatoes, such as beefsteaks and the large-fruited heirloom tomatoes, are more prone to cat facing than small-fruited varieties.

Normally, tomatoes that are disfigured from cat facing are still edible however they may ripen unevenly and they can be difficult to slice – I just chunk them up instead! Still delicious!

Black mold

Black mold started growing in the growth cracks of this tomato.

Black mold started growing in
growth cracks of this tomato.

Black mold is caused by various fungi (including Alternaria alternata) that attack tomato tissue that has been injured in some way. It is rarely found on healthy, unblemished tomatoes. The fungal spores usually enter the tomato where the skin has cracked or where insects have caused injury to the fruit. As the fungus grows, it creates brown or black sunken lesions which expand and eventually cause the whole tomato to rot.

If you catch it early, you can just cut out the bad patches but it’s important to remove all the soft tissue or the tomato will taste bad.

All of these problems have developed on at least some of my tomatoes this season. Fungicide sprays listed for use in vegetable gardens can help but I normally don’t bother with them. None of these diseases have caused any major damage to my tomato crop. We just harvest the blemished fruit, cut out the diseased parts, and eat them. You should NEVER can or freeze tomatoes that show signs of disease.

Even though our tomato crop hasn’t been a bust this year, the yield from our 36 tomato plants should have been much higher. I’m normally swimming in tomatoes at this point in the season. Well – at least the tomatoes we’ve harvested have been very tasty. I’ve been able to can a few batches so far and they are still coming along. Hopefully this hot spell we are in now will give them a late season boost!

Lynne's cherry tomatoes are beautiful but her other tomatoes are small.

Lynne’s cherry tomatoes are beautiful
but her other tomatoes are very small.

How did your garden do this year?

My sister Lynne in Vermont told me yesterday that her tomatoes are all really small this season compared to other years. It’s been unusually cool up there this summer, too!

She sent this photo of her recent harvest. Nice rattlesnake beans and cukes Lynne!

Until next time –

     Happy Gardening!

Pickleworm entrance holes in zucchini

I didn’t notice the little holes when I cut the squash from the vine. It wasn’t until they had been sitting in the harvest basket on the kitchen counter that I noticed the little pile of frass (insect “poop”) on the outside of one of the zucchini that I had harvested. It looked like pale green sawdust piled just outside a small hole in the squash. When I picked it up, I noticed that there were quite a few little holes in this particular zucchini.

Hmmmm – pickleworms!

Pickleworm on pumpkin; Gerald Holmes, California Polytechnic State University at San Luis Obispo, Bugwood.org

Pickleworm on a pumpkin

Interestingly, just a few days before, I had received a post on our discussion board inquiring about the same problem with pumpkins:

How soon can pumpkins be cut from the vine? I have trouble with something boring holes in them causing them to rot if left on the vine too long.

Pickleworms (Diaphania nitidalis) are pests of pumpkins as well as various types of summer squash, cucumbers, and cantaloupes. They literally devour the fruit from the inside.

Pickleworm larva feeds on the tender flesh of a zucchini

A pickleworm larva feeds on the
tender flesh of a zucchini

These destructive pests are the larvae of a moth that doesn’t even survive in this area over the winter. They are subtropical insects and spend the winter in areas like Florida and Texas. In the spring, they migrate northward to invade vegetable gardens as far north as southern New England and parts of the Midwest. The only blessing is that it takes them a little while to make it up here so one way to avoid them is to plant squash crops as early as possible and/or plant early maturing varieties so you can harvest a nice crop before they become prevalent. That is easier to do with summer squash than with cantaloupe and pumpkins, though.

Unfortunately, pickleworms have a very short life cycle (often less than 30 days) and can produce up to 4 generations per year depending on the climate. In our area, I doubt they have more than two or three generations but this is still enough to wreak havoc in the garden.

It’s the larval stage that does all the damage. The young pickleworm larvae/caterpillars begin feeding as soon as they hatch from their tiny eggs. At first, they bore into and feed on the flower buds and the tender young stems of the plants. As these caterpillars grow, they molt several times going through 5 larval instars before they mature and pupate.

Small entrance holes mark where the pickleworm caterpillar has bored into the fruit.

Small holes mark where the pickleworms have bored into the fruit.

The major damage comes when the older pickleworm larvae bore into the fruit. The small entrance holes they make are tell-tale signs of the invasion. Sometimes you will see little piles of frass on the fruit just outside the holes. Inside, these caterpillars are voraciously consuming all the good stuff – hollowing out the interior and leaving the fruit inedible.

The other day I cut open a medium-sized zucchini and found a large green pickleworm inside. This was quite a surprise since I hadn’t noticed the entrance hole.

The caterpillar left a large cavity where it had eaten the flesh of the squash. Later, I found a smaller zucchini that had at least 5 bore holes in it so there were probably 5 pickleworms inside. Gross! I didn’t look!

Chowing down on my zucchini!

Chowing down on my zucchini!

Over the years, we haven’t had much trouble with these disgusting caterpillars. Thinking about it now, this is probably because normally by this point in the season (when pickleworms begin to be a problem), my summer squash plants have succumbed to squash vine borers and I have pulled them all out! I got lucky this year and the vine borers only got a few of my plants. So now we have pickleworms. Ugh!

I do think that the pickleworm population must be worse this year because I also found them in both of the cucumbers I just picked. That’s a first for me but I have heard of some people losing almost an entire crop of cucumbers to these nasty critters. Because summer squash is their food of choice, one suggestion to help protect cucumbers is to plant a trap crop of summer squash beside the cucumbers so that the pickleworms attack the squash and leave the cucumbers alone – this is supposed to work pretty well.

Other control methods

In our area where pickleworms can’t overwinter, the best bet is to plant resistant varieties and early maturing varieties of squash and to plant these crops as early as possible. Starting the seeds indoors and planting hardened off plants can help you get a jump on the season. That way you can usually get a nice harvest before these caterpillars become prevalent. For us, they are normally a problem later in the season. I am just now seeing them.

This cucumber is a goner!

This cucumber is a goner!

Normally pickleworms are difficult to control with pesticides because once they bore into the fruit, they are protected from sprays. Timing is critical; you have to control them when they are first hatching out.

When the buds first form and the flowers begin to open, spray the plants with Bonide Bt Thuricide or Bonide Captain Jack’s Deadbug Brew which contains spinosad. These products are normally less harmful to beneficial insects when used according to the label directions.

Pickleworms can also be controlled with Bonide Eight sprayed according to the label directions.

Always spray the plants early in the morning or in the early evening when the bees are less active. Pay close attention to the pre-harvest interval (PHI) when spraying vegetables.

Boy, am I glad they don’t like tomatoes!

Until next time – Happy Gardening!

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