West central Michigan vegetables regional report – July 10, 2013

Insect and disease activity are picking up in west Michigan vegetable crops.

Asparagus plants continue to develop in fields where harvest ceased the week of June 23. I have not observed cladophylls (needle-like leaves of asparagus) develop yet, but this should happen soon if it has not already. Once plants have developed leaves, it is important to apply a protectant fungicide and begin a regular spray program. Fungicides can be timed using weather data from in-field weather sensors in combination with the TomCast disease model. Michigan State University Extension advises that with recent wet weather, conditions are favorable for diseases such as purple spot, which can defoliate fern. Japanese beetle adults have become active in the last week.

Significant aphid populations in celery were again observed in a southwest Michigan location and in Kent County over the past week. Crinkled, curly leaves can occur with aphid feeding. MSU entomologist Zsofia Szendrei’s trials have shown that the insecticide Movento (a.i. spirotetramat) provides excellent aphid control, outperforming all other tested compounds if it is applied with a non-ionic, penetrating surfactant such as Dynamic or Silwet. In a grower’s field, the efficacy of a recent application was evident, with dead aphid carcasses present on plants.

Celery leaf tier has been detected as of this week; this caterpillar makes shelters out of leaves using webbing. Harvest of celery planted early under low-tunnels was starting last week.

Dead aphids
Dead, brown aphid carcasses on celery after application of
Movento (a.i. spirotetramat). Photo credit: Ben Werling, MSU Extension

For cucumbers, spray programs for downy mildew should begin now as spore captures in MSU traps have increased. Visit Mary Hausbeck’s lab website for links about management and monitoring. For cucurbits in general, I observed squash bug adults and egg masses in an Ottawa County cucurbit field yesterday (July 9). For pumpkins, if plants are flowering, a threshold of one egg mass per plant can be used to decide if an insecticide application is warranted. Prior to flowering, a spray is warranted if squash bugs are present and plants are wilting. Pyrethroids can be used for control. Zucchini harvest is ongoing in Ottawa County as of this week, and will begin soon in Oceana County.

Squash bugs
Squash bug egg masses are laid on the underside of leaves, often
where two veins come together to form a V.
Photo credit: Ben Werling, MSU Extension

Onions had six to eight leaves in a Kent County location this week. Spray programs for diseases and thrips have been ongoing for the past few weeks.

In sweet corn, over the period of June 28 through July 5, I captured 10 corn earworm moths in a Hart, Mich., pheromone trap. Some sweet corn plantings are silking now in both Kent and Oceana counties, and are attractive to egglaying females that lay eggs in the silks. Timely sprays, whether organic or conventional, are key for control of this pest. Material needs to be on silks prior to egg hatch or caterpillars will move into the ears where they are protected from sprays. It is key to use spray equipment that will propel insecticide down to the ears and cover silks.

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