Insects! Plant it and they will come. Or not.
In a research farm setting, unlike a commercial farm, we actually WANT pests to show up so we can conduct a trial. But sometimes we plant it and they don’t come… In fact, there’s a joke that if you want a pest to disappear for a season, just get a graduate student to start a research project.
Maybe because there aren’t any graduate students associated with this project, the insects, namely striped cucumber beetle and squash bug, showed up in impressive numbers this season.
Striped cucumber beetle. Organic squash growers know that there is not currently an effective insecticide for striped cucumber beetle that’s allowed in organic production. Like many growers, we used kaolin clay as a preventive treatment to deter feeding. Plants in the organic IPM subplots were treated with kaolin clay weekly until they reached the five-leaf stage when they become less susceptible to the bacterial wilt that striped cucumber beetles can transmit through their feeding. Because the plants in the different treatments were growing at different rates, the cultivated and black plastic treatments got one application, the straw mulch got two, and the rolled rye needed four.
Squash bug can be especially tricky to work with in a research setting because there’s no guarantee that they’ll make an appearance in your plots, and also because they lay their eggs in masses of 10-30, so their distribution can be clumpy and difficult to quantify.
The team started finding adults and egg masses when scouting in early July and that continued. They chose a threshold of 0.5 egg masses per plant because their planned insecticide (a pre-mix of pyrethrins and azadirachtin from the neem plant), kills at best 60-70% of the bugs. Because most insecticides are not effective against insect eggs, they- the team, not the bugs- waited until most had hatched. The first application went on July 31st, with the goal of finding a sweet spot between letting as many eggs hatch as possible, and not letting the early hatched nymphs get too big. Larger immature insects are harder to control than smaller ones. Egg masses remained over threshold in early August and warranted another application when those eggs hatched.
And then there’s… Beneficial Insects!
One question for the trial was how treatments might affect the type and number of beneficial insects and other arthropods, so when they scouted for pests, they also recorded beneficials.
Some beneficial insects actually use squash bug as a host. One, Trichopoda pennipes, is a fly in the family Tachinidae that lays its eggs on the surface of adults and nymphs. The eggs hatch and the fly larvae feed inside the squash bug, eventually killing it. They saw plenty of adult flies, with their distinctive orange abdomens, as well as eggs deposited on adults and nymphs. Learn more about Trichopoda pennipes here
Another beneficial found feeding on the nymphs was lacewing larvae. Lacewings are ferocious little predators that will wrestle down and eat almost any soft-bodied insect smaller than them. Surprisingly, most of the lacewing larvae were brown lacewings, rather than green lacewing eggs and larvae. Learn more about brown lacewings here.
Other beneficials found regularly were damsel bugs, lady beetle adults and larvae, and Orius adults and nymphs. The lady beetles and Orius became more common as aphid numbers started to increase late in the season.
Next up? We look at how researches managed diseases, and finish with a look back over the season.