Q&A: Why do my cucumber and zucchini plants wilt?

One Spotted and multiple Striped Cucumber Beetles, feeding on overripe pumpkin. Photo: Whitney Cranshaw, Colorado State University, Bugwood.org

Q: Last summer I had cucumbers and zucchini wilting and dying even though I’m pretty certain I didn’t have root rot or squash vine borer. What should I try this year so I can hopefully get a harvest?

A: Bacterial wilt disease, transmitted by cucumber beetles is the prime suspect for crop failure in this instance. Both of these garden pests – Striped Cucumber Beetle and Spotted Cucumber Beetle – are native to North America and can cause serious damage to vegetables in the squash/cucumber family, though they can also feed on unrelated fruits, vegetables, and ornamental plants.

Although their feeding causes direct plant damage, the main issue comes from their introduction of one or more plant pathogens. These beetles can transmit diseases like bacterial wilt and viruses, none of which are curable.

Delaying the planting of squash and cucumber transplants until mid-June may evade the host-seeking adults. Until they bloom, cover plants with insect netting or row cover (the former is ideal as it doesn’t trap heat). Bees will need to reach the flowers for pollination, but once the fruits start to develop, plants tend to be less susceptible to infection. Since more than one beetle generation can occur per year, clean-up veggie garden debris in autumn to deny remaining adults overwintering shelter.

For now, ‘County Fair’ is the only available variety resistant to bacterial wilt. This pickling cucumber is parthenocarpic– it produces mostly female flowers that don’t require pollination to set fruit. The Cucumber Beetles page at the Home & Garden Information Center has more information about these insects and their management.

By Miri Talabac, Horticulturist, University of Maryland Extension Home & Garden Information Center. Miri writes the Garden Q&A for The Baltimore Sun. Read more by Miri.

Send home gardening questions to Ask Extension at the Home & Garden Information Center

Plants not behaving as expected: vegetable garden edition

Two of the vegetable crops I grew this year are known for loving the heat: okra and eggplant. I grow eggplant in pots on my deck, to avoid flea beetle infestation, and okra directly in the ground in my community garden plot. Both of them produced adequately over the summer. Now it’s fall; we’re having days in the 70s and nights in the 50s, and there are fewer hours of sunlight in the day. Time to pull the summer crops, right?

Except – boom! Both the okra and the eggplant are going gangbusters. More flowers, more fruits than in the hot summer months, by far.

‘Bride’ eggplant on a cool autumn morning

So why aren’t these plants following the rulebook? Do they not know how to read? Or have the rules changed?

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Squash vine borers and squash bugs: two garden villains!

My squash and zucchini have been breeding grounds for these two garden pests in past years. They also have confused me because I tend to conflate the two or have mixed up which one I’m searching for information on online. This year, despite taking more steps to combat both of these evil-doers, my garden still took major hits from this duo.

In anticipation of this insect onslaught, I took the following extra steps:

  • I kept the young squash and zucchini plants under floating row cover until they flowered. I uncovered then so that pollinators could get in and do their thing. I potentially could have kept them under cover longer if I manually pollinated, but the plants were growing beyond the cover structure I made, so it was time.
  • I wrapped foil around the lower stems of the plants as HGIC suggests to prevent egg-laying.
  • I searched for and removed more regularly squash bug eggs found under the leaves.
  • I planted these crops in a bed that had NOT yet been used for squash or zucchini and therefore hopefully would not contain overwintering vine borers in the soil.
  • I planted yellow squash, zucchini, and, HERE COMES A NEW CHALLENGER: TROMBONCINO SQUASH! The tromboncino variety is supposed to be vine-borer resistant.

The following is my garden’s tale of woe, and my future plans for growing a squash bug and squash vine borer-free garden.

Let’s start with the one that has been the most visible to me, the squash bug.

Squash bug

For the past few years, I’ve been seeing these guys’ eggs on the undersides of my squash, zucchini, and cucumber plants. When I find them, I tear off the small section of the leaf, smash ’em between my fingers, and chuck them away. I kept doing this, but kept finding more this year. I’m sure tons of the eggs got past me.

Confirming that notion, I did later catch these nymphs having a party on my plants.

Squash bug nymphs
Squash bug and eggs

In my garden at least, I don’t believe the squash bugs are the main villain destroying my squash and zucchini crop. I saw some stippling on the leaves here and there, but nothing that seemed to do severe damage.

Squash bug and stippling on leaf
Squash bug and stippling on leaf – this was about the worst damage I saw like this.

One of my later tromboncino fruits had a ton of superficial damage on it. My guess it is from the squash bugs. They didn’t touch any other tromboncino fruits, and this particular one was closer to ground level, while most of the rest of my tromboncino crop was high in the trellis. Are these guys afraid of heights?

Squash Vine Borer

Previously, in my gardening efforts, I’ve had zucchini and squash plants succumb to the squash vine borer, and I took several steps to avoid them again this year, but to no avail. I’m sorry to say, both our zucchini and squash plants grew large and healthy, produced a round of solid fruits, then quickly wilted and died within a couple weeks of each other.

Tromboncino squash on trellis
Tromboncino squash climbing up it’s trellis, making fruit, and not worrying about any bugs.

I did not see any adult vine borer moths, but I found a big fat larva in the dead plant’s stem. I tore out the dead/dying plants.

While yellow squash and zucchini were out for the count, the tromboncino kept on truckin’ and had no issues so far with either of the nasty bugs other than the one damaged fruit.

What else can I do?

There are more means of combating these bugs if I decide to do battle with these villains again:

For squash vine borers (info mainly from the HGIC page):

  • Adjust the timing of planting. Planting early or late in the season to attempt to avoid the life cycle of the vine borer. Or, plant in succession; stagger when we plant so if some crops get taken out, you still have another coming along with more fruit and another chance at success.
  • Do surgery on the stems of the plant you fear is infested, rip out any larva, and mound up dirt over wounded stems to induce supplemental rooting.
  • Spray lower stems with spinosad or pyrethrum.
  • Spray lower plants stems and base of plant with pyrethrins when adults are flying (mid-late May). Repeat 14 days later. Or sprinkle diatomaceous earth on lower stems. 
  • Bt (Bacillus thuringiensis) or beneficial nematode Stinernema carpocapsae can be injected into wound to kill borers.
  • Seal up infested vines in plastic bag before larvae pupate (break life cycle).
  • Plant resistant crops: Butternut and cushaw are resistant; yellow crookneck is less susceptible than zucchini. (I went for the tromboninos).

For Squash bugs (info mainly from the HGIC page):

  • Neem, horticultural oil, and insecticidal soap are effective when sprayed directly on nymphs. Adults are very difficult to kill with the insecticides available to home gardeners.
  • Trap adults and nymphs by placing boards near host plants under which they will hide. Lift boards and destroy bugs in the morning.
  • Bugs also hide under mulch. When numbers are high, mulch may need to be removed.
  • Removing all plant debris at the end of the growing season is essential.
  • Check seed catalogs for cultivars of summer and winter squash that are resistant to squash bugs.

What will I actually do?

I’m gonna give up!

This is at least the third year in a row with a similar story for the yellow squash and zucchini in my garden, and I think I’m done with regular yellow squash and zucchini for a bit. There are more things I could do to mitigate the problem, but I’m tired of providing food for these buggers, and I’m not into high-maintenance gardening, so I’m gonna call it quits on those crops for now.

Besides, the vine-borer-resistant tromboncino squash crop I tried this year has excelled, and it cooks and eats pretty much like its susceptible cousin crops. I plan to keep going with tromboncino. Maybe a year or two without fodder for these bugs will break the cycle and allow them time to die off or move elsewhere.

Here are two great videos on both of these problem bugs:

Feel free to take a look at my posts from last year’s growing season.

Dan Adler
HGIC Web Support and Video Production

DIY garden structures with materials you have on hand

I had a lot of goals for improving my garden since last year’s adventure which meant new things to build! However, with the current prices of lumber and materials, plus my only basic carpentry skills, I didn’t want to go all out creating beautiful, sturdy, perfect designs and structures from new materials purchased specifically for these builds.

I wanted to quickly build tomato support, floating row cover, a large trellis for climbing plants, deer fence, and a garden gate all without spending too much at the hardware store or spending a ton of time planning. That meant largely using scrap wood I had laying around or cheap materials like PVC, and going for it.

MEGA TRELLIS

I’m trying tromboncino squash this year which really climbs, and I also wanted to allow cucumbers to climb, so I thought I’d build some sort of large support object. I had a bunch of 2×2, 10 ft long lengths of wood left from contractor work in my basement and thought that would be good material. I wanted something tall that I could walk under and pluck vegetables from. Plus, I wanted it to be non-permanent.

I decided to make this ladder-like structure with a hinge at the top so that I can collapse it and store it in the garage without taking up a lot of space. I bought a metal threaded rod, drilled holes through the wood at the ends that would make the apex of the structure, and ran the rod through those holes to make a hinge. The rest is built with wood screws. Metal eyelets were screwed into the wood so that I could run twine crisscrossed through the structure to allow plants to climb.

The structure was a bit wobbly on its own since it is so tall and not wide, so I worried about it getting blown over during a storm — especially with leafy plants acting as sails. I tied rope to two cinder blocks that pull down and away to give it more stability.

Fence panel tomato hangers

I saw these cool tomato clips online; you can have some sort of structure to hang a string from, then use these clips to fasten joints of the tomato plant to the string to hold it up. With these, all I would have to do for tomato support is to make some sort of triangle or tripod with a high point I could tie string to. It seemed like a simple way to build something. Also, I liked the way my trellis folded flat for storage.

Again, leftover from contractor work, I had some parts of wood fencing from a recently replaced segment of fence I had done. I took off a bunch of the boards, leaving the two outside ones connected by the horizontal segments, and connected two of the removed boards to the others via hinges at the top. I added more horizontal support at the top and bottom, then added eyelets at the top crossbar to tie rope to. This fits right in my 4’x4′ tomato bed. The strings hang down and with the clips, hold up the tomatoes.

Easy PVC piping structures

I went to the hardware store and picked up several lengths of 5 ft white PVC pipe and a handful of T connectors. I didn’t have an exact plan, and I probably should have bought a bit more of everything, but I was able to start with building floating row cover for some of my squash, and then when that wasn’t needed, I reconfigured it into support for my tomatoes.

Collapsed tomato structure
Collapsed tomatoes

I cut the pipes: some in a third and 2/3 lengths. Connecting them with the T connectors, bending, and wedging the ends of the pipes into the corners of the raised beds, I was able to make an archway over my 4ft square section of raised bed. For floating row cover on squash, I draped row cover fabric over it and pinned it down with bricks around the edges. For tomato support, I drilled a few holes, screwed eyelet hardware in, attached twine, and used tomato clips to hold up tomatoes.

The 1/2in pipe is a little flimsy, and I ran out of enough pipe to make as much support as I wanted.

I left on vacation for a week and came back to totally collapsed tomatoes. No big surprise there. This design is good for row cover, but not for tomatoes beyond a certain point. I need stronger materials for this one.

After the PVC failure, I wanted a quick way to build something that would hold up the tomatoes. I’m running low on quality materials, so I made this unimpressive support out of two fence panel boards, and the other longest piece of scrap wood I had around. Two wood screws connect them at the top. I don’t think I will keep this for next year as it isn’t collapsible, isn’t that sturdy, and I would hope to make something better if I need something next season. Clips were used again to hold up the plants.

Micro deer fence

I’ve got one 4’x4′ raised bed segment with corn in it that got devastated last year, presumably by deer. Originally this year, I was planning on building a tall deer fence around my entire garden area, similar to this one. I understood that the fence doesn’t need to be particularly strong – just tall enough they couldn’t jump it.

Then I had the idea, “Dan, you clever guy – why don’t you fence ONLY the corn and save a lot of effort!” So I decided to make a tall, twine fence around just the corn.

Again, with leftover fencing boards, I just screwed four of the boards vertically to the walls of the raised beds, tapped some nails in them for string, and wove twine around the whole thing.

It was soon after I finished stringing this thing up that I realized the error in my logic (most readers here were probably yelling at their screens): yeah, a deer cannot jump into my corn field, but they sure could stick their snouts through the gaps in the twine and much fairly unhindered.

I mused about stapling a segment of the rodent fence material used for the outer fence around the four boards, but in the end, laziness and the sense of experimentation helped me decide to leave it as-is and see what happened. Perhaps the deer would be weirded-out enough by the twine to leave it alone.

As of this writing, we are beginning to harvest corn, and it hasn’t been touched which is further than we got last year. Fingers crossed this trend continues.

Building is fun

It’s been fun building. I’ve done this all without breaking out a ruler or tape measure! Mostly, it’s hammer, nails, wood screws, drill, and string that I’m using. Nothing fancy. Luckily, produce does not care if all corners are square, and good enough is generally good enough if you don’t have to support more than a couple plants.

The last item I’ll mention is a little gate panel built from the absolute last pieces of the 2×2 wood. I didn’t even have enough to make a diagonal cross piece that went from corner to corner. I stapled a bit of wire fencing onto it and put a slide bolt to shut it. My wife was tired of having to hop the wire fence to get into the garden, so this was the solution. Again, not strong or beautiful, but it works.

Vegetab

Feel free to take a look at my posts from last year’s growing season.

Dan Adler
HGIC Web Support and Video Production

Semi-novice Gardener – Raised Bed Vegetable Garden Adventure (vol. 3)

Hi all!  It’s time for check-in #3 on my summer gardening efforts.  Overall, things are going well, but there have been big ups and downs.

The new raised bed we built is doing well.  Krysten planted corn in the center one, and a couple cucumber seedlings in the rightmost one.  The cucumbers have been slow to develop and grow.  I think this is because of the extreme heat.  In the last week or two, one’s growth has accelerated and it’s finally growing one nice cucumber.  I may harvest it and slice it up to use as an ingredient in a nice summer cocktail drink tonight (It’s Friday as I write this draft!). Do a web search for “porch swing” cocktail recipes.

Since we got the fencing up that encloses the whole space, we have had 0 evidence of animals munching our crops!  Huzzah!  However, we DID see one deer in our yard and it was eating our hostas elsewhere on our property (and has continued to; the hostas are mostly gone now).  So, we DO have deer, but they haven’t been interested in our vegetables (yet).  I wonder if they don’t like walking on the gravel we have down?

Tomatoes

We have been harvesting a lot of tomatoes! One of our plants grew very large and tall and ended up flopping over the tomato cages we built in the last update.  We needed something taller!  We were worried that the tropical storm in the first week of August was about to topple the biggest one completely, so we hurriedly built an extension.  We found some scrap wood in the garage, attached it vertically to the sides of the raised bed, and strung twine around nails in the boards back and forth from board to board.  This seems to hold it up well and while the tropical storm wasn’t too bad here, there was no damage afterward.  We need to do the same for our second largest one this weekend.

Taller tomato support
Taller tomato support

The early blight issue I spoke about in the last update has seemed to be controlled by pruning more heavily and keeping air flowing.  However, our smaller tomato plant has been slow to fruit and has some holes/spots on the leaves.  After perusing the HGIC site, my guess was that it was Septoria leaf spot which is a fungal disease, however as a couple knowledgeable HGIC coworkers proof-read this post, they said it was actually most likely from flea beetles. It may sound like I’ve got the inside connection with experts, but everyone can send in questions to our Certified Professional Horticulturists for help like this!

Septoria leaf spot on my tomato plant
Flea beetle damage on my tomato plant

There are prevention and control directions on the HGIC page for flea beetles, but since the damage isn’t large at the moment, I think we’ll leave it as-is now, and plan to clean up and remove garden debris to reduce overwintering sites for the beetles when we wind down the growing season this year.

Overall though, we’ve been harvesting more tomatoes than we know what to do with, so we’re happy with our tomato efforts here! I’m considering making a whole lot of sauce.

Tomato harvest
Tomato harvest

Squash and zucchini

In the last update, I mentioned I suspected squash vine borer larvae to be killing my zucchini plant from the inside.  I did the surgery and discovered I was right.

Squash vine borer larvae in zucchini plant
See the white larvae in the center, lower third of the image?

I remember reading on the HGIC site at some point that in general with cucurbits, you can cover parts of the plant that grow above the soil with soil, and they will begin to root.  I cut the plant to disconnect the borer-infested segment (which was pretty much down into the roots) from the good parts.  I ripped out the roots and infested stuff, then planted the remaining stuff back in, mounding soil over it.

For a few weeks, things seemed promising.  Most of the large leaves did not make it, but some younger and new leaf sprouts were growing strong, and a small fruit started growing.  This suggested to me that after some time, we’d likely have this zucchini plant back from the dead and producing again.  However, that little fruit died and rotted, and the leaves and stems suddenly showed damage.

Our squash had been doing great.  It kept producing great fruit at a rapid pace, and kept expanding.  It was healthy; not showing damage from squash vine borers or cucumber beetles like the zucchini had.  It expanded outside of the raised bed and sometimes those leaves would appear wilted.  We assumed it was because of the extra heat from the gravel and the hot sun.

All was going well until a few days ago – it began wilting everywhere and wasn’t recovering.  Fruit production stopped.  We took a closer look, and we’re seeing the same squash vine borer type damage we saw with the zucchini!  Noooo!  It looked pervasive.  I wasn’t about to do more larvae extraction (it was gross, and squash isn’t my favorite vegetable).

So, we called it on both the zucchini and the squash plants.  2:35 pm, Friday, August 10th, 2020.  We ripped them out and tossed them far from the garden.  We’re making space for some sort of cooler season crops (the planning hasn’t started yet).

Next year, we are absolutely taking the following prevention steps (taken from the HGIC page on squash vine borers):

  • To prevent egg-laying, wrap a collar of aluminum foil around lower stems or dust or spray lower stems with spinosad or pyrethrum.
  • Cover plants with floating row cover until flowering.
  • Plant early to lessen injury. Use transplants instead of seeds. Or, plant squash seed mid-June.
  • Butternut and cushaw are resistant; yellow crookneck less susceptible than zucchini.

Green beans

We’ve been harvesting a few green beans from the mature plants that survived the rodent massacres that happened before we got the fence up, but it wasn’t enough to make a meal out of.  Several weeks ago, I planted more seeds to replace the eaten ones and those have grown and should be fruiting soon.  I hope that we can have some dinners with roasted green beans soon; they are my favorite of our garden veggies after tomatoes (and since tomatoes are fruit, I could say that green beans are my favorite veggies).

The zinnia we planted in the center of the green beans has gotten large and is crowding them.  We will likely try to tie it up to keep it more vertical than horizontal.

There are a couple bean leaves with holes munched out of them from some insect, but nothing to be too concerned about yet.

Moving forward

We’re still having fun with the garden.  It’s great to be done building for the most part.  Krysten has been adding a few pots on the outskirts with flowers in them which makes the space look nice.  I think in the next season, we’ll probably add more flowers in pots and save the beds for the vegetables.  The flowers have overcrowded vegetables in some instances in the raised beds, and we should be able to attract pollinators close enough to the vegetables via potted flowers.

I’m looking forward to more tomatoes and our first meal with green beans.  Perhaps in the next update, I may present our plan for cool-season crops.

View previous updates:

Dan Adler
HGIC Web and Communications Manager

Resisting Mosaic Viruses in Cucurbits

I grow most of my vegetables in a community garden plot: sunny, cheerful, with soil I’ve been improving with free compost for years now. It’s a good situation, but while community gardeners can share labor, tools, plants and seeds, they also end up sharing pests and diseases. Our garden has been suffering from a problem I never encountered at home or in the Derwood demo garden: mosaic virus on cucumbers and squash. Mostly I have dealt with this problem by the highly scientific method designated Not Even Trying, but this year I really want to succeed. So, some research!

Figure 1. Pumpkin plant infected with watermelon mosaic virus (WMV)
Photo by Dr. Gerald Brust of watermelon mosaic virus on pumpkin. Wait, what?

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