The author’s daughter picking Colorado potato beetles from potato plants.
For the past 11 years, I have grown my vegetables in a community garden plot, which has provided a rough, real education in plant pests, diseases, and weeds. Why? Because these mega veggie gardens are pest hot spots, and late summer is the worst time of year for the beasties. Whether it be my beans, cucumbers, tomatoes, or eggplants, the “bad” insects abound–threatening to destroy fruits and foliage and often spreading disease as they munch and crunch along. You just have to keep fighting them with every tool in the toolbox. And, if the bugs beat my crop, I will often start again, if there is time and the season allows. Sometimes beating the pests is just a matter of retooling planting time.
The five most common vegetable garden pests that I battle in mid- to late-summer are Colorado potato beetles, striped cucumber beetles, eggplant flea beetles, Mexican bean beetles, and harlequin cabbage bugs. Each returns year after year with regularity, but some years are worse than others. The severity of the previous winter usually indicates the severity of my pest problems–the milder the winter, the harsher the pest problem. Last winter was pretty mild, so this summer the pests and rampant. Here are some ways that I have learned to overcome these pests.
Colorado Potato Beetle
Colorado potato beetles mating on top of a potato plant.
The surest way to attract Colorado potato beetles to your garden is to plant potatoes, but if you don’t have potatoes, they will go for your tomatoes and eggplant secondarily. (Fortunately, they don’t appear to be attracted to my tomatillos.) The fat, striped adult beetles emerge from the soil and nearby forested areas to feed on emerging potatoes and then lay clusters of orange-yellow eggs on leaf undersides. These are followed by highly destructive little orange larvae that eat foliage and grow very quickly. You can kill the insects at any stage, but it’s easiest to pick off the adults and eggs. (Click here to view the full life cycle of these beetles.) The beetles can complete up to three life cycles in a single season, so once you have them, you generally have to fight them all summer.
Colorado potato beetle larvae (left) on tomato.
These insects are highly resistant to insecticides, so it pays to choose organic methods of control. Time and time again, well-timed cultural control and good winter cleanup have proven to be the best means of battling them. Cultural control is essentially “picking”off the adults, eggs, and larvae and/or pruning off egg- and larval-covered leaves and branches. I generally smash picked specimens, but you can also drown them in a bucket of water. Good picking should start early and continue until all signs of these pests are gone.
(To learn everything there is to know about Colorado Potato Beetles, visit potatobeetle.org.)
Striped Cucumber Beetle
The symptoms of bacterial wilt spread by striped cucumber beetles.
As their name suggests, these beetles favor cucumbers, but they also attack melon vines. Small, striped cucumber beetles look so cute and innocent, but they are so destructive. Every year my cucumber crop is a crap shoot, even if I choose tough hybrid cucumbers. These beetles cause damage by feeding on the plants and fruits, but the larger problem is the catastrophic bacterial wilt that they spread from plant to plant. Once cucumber vines get cucumber bacterial wilt, there is no turning back. The leaves will start to show droop and eventually whole stems will collapse and the vine will die.
These pests may have two to three cycles in a season and are next to impossible to control, even with harsh chemical insecticides. Floating row cloth cover can keep them at bay, but it is a hassle and does not allow pollinators to reach the plants. For me, the best course of action is to choose bacterial-wilt-resistant cucumber varieties. Cornell University Extension offers a great list of resistant cucumber varieties to choose from. Of these, I have grown the short-vined slicer ‘Salad Bush‘, which is great for container growing. Two more reliable varieties are ‘Marketmore 80‘ and ‘Dasher II‘.
(Click here to learn more about striped cucumber beetles.)
Eggplant Flea Beetle
Eggplant flea beetle damage on an eggplant leaf.
Tiny jet-black eggplant flea beetles are the smallest summer pests in this list, but they can devastate an eggplant in a matter of days. The small but numerous insects leave little pock marks all over a host plant’s leaves. Badly damaged leaves barely photosynthesize, resulting in poor, weak plants that produce puny fruits.
If you want to grow eggplant, you have to protect them from eggplant flea beetles. There are plenty of insecticides that will kill these insects, but only a few non-chemical cultural practices will stop them. The best method that I have found is protecting plants with summer weight floating row covers that transmit a lot of sunlight while physically keeping insects from the plants. The key is covering plants early and then securing the row covers at the base, so the tiny beetles cannot crawl beneath them. Holding cover edges down with bricks, pins, and even mulch or compost, works. The only caveat is that you may need to hand-pollinate plants for fruit set.
Good fall cleanup of infested crop plants will also keep populations down from year to year. On average, eggplant flea beetles will complete up to four generations in a single season.
(Click here to learn more about these pests.)
Harlequin Cabbage Bug
Harlequin bug adults and damage on summer broccoli.
These ornamental stink bugs are the worst enemy of summer kale, broccoli, and other crucifers. They suck the juices from the leaves causing pock marks all over them. The most striking destruction I have ever witnessed was with an enormous Portuguese kale that I had nurtured to a bold 2′ height through spring. Once the numerous beetles started to attack in early summer, the plant had no chance. I sprayed organic pesticides on the hundreds of adults that covered the plant to no avail.
There are a few management practices that will help stop these bugs. Floating row covers can also be used, as was suggested for the eggplant flea beetles, but harlequin cabbage bugs are big enough to pick off by hand, if you have the time and can handle the slightly stinky smell they emit when disturbed. Small nymphs are also susceptible to treatment with insecticidal soap.
Two to three generations of harlequin cabbage bugs can occur each season. By late summer, they are no longer a problem, so you can plant your fall cabbages and kales with confidence.
(Click here to learn more about these pests.)
Mexican Bean Beetle
Mexican bean beetle larvae and damage on a bean leaf.
Like Colorado potato beetles, it’s the larvae to Mexican bean beetles that do the harshest damage to bean plants. The adults emerge in late spring but they rarely cause major problems on bean plants until midsummer. The adults are orange, black-spotted beetles that lay clusters of orange-yellow eggs below the leaves, much like the Colorado potato beetle. The unusual larvae are fuzzy, bright yellow, and skeletonize leaves as they feed along the leaf bottoms.
Mexican bean beetle adult on a bean leaf.
You can control these pests as you would Colorado potato beetles with one exception – destructive harvesting. Destructive harvesting is the harvest and total removal of infested plants from the garden. After picking, infested plants should be pulled, bagged, and taken far from your garden. (Click here to view a YouTube video from the University of Maryland about destructive harvesting.) Beans can be replanted as late as mid August for early fall harvest.
In general, regular weeding, good plant care, and excellent garden clean up, in summer and fall, will help keep pest populations down. Clean the ground of all leaf litter and weeds, and amend the soil with top-quality amendments for vegetables, such as Fafard®Garden Manure Blend or Natural & Organic Compost, and your plants will be more robust to resist the many garden pests that threaten to destroy them.