West central Michigan vegetable update – June 6, 2018

Asparagus harvest has slowed with cool weather, but is ongoing. Pest and disease activity is continuing.

Pines near field
Asparagus beetle problem fields are often bordered by pine trees. Beetles have been overwintering in crevices in tree bark. Good overwintering sites can harbor a large population ready to emerge in spring and move into asparagus. Beetles do not reproduce in pine trees (they only lay eggs in asparagus), and reproduction with commercially harvested fields is also minimal because spears with eggs are being continually removed before larvae can hatch and become adults. Photo by Ben Werling, MSU Extension.

Asparagus harvest slowed with recent cool temperatures. Tip quality has improved with recent cooler weather and the rains, and farms I visited yesterday, June 5, hoped to continue harvesting another two to three weeks. At the research farm, it was noted that tip quality has not recovered as well as would be expected after the recent cooler, wet weather, though diameter and yield seem typical for this time of year.

Purple spot lesions were visible on the main stems of a young field I visited yesterday. Rainy and cool weather are ideal for discharge of spores from overwintering structures onto main stems. These primary infection sites can produce spores that lead to “secondary” spread of the disease on the leaves of plants, which can cause problems later in the season. Protection of young plantings with chlorothalonil-based fungicides can help prevent secondary spread of spores from stem lesions to newly emerging leaves. Mancozeb-based products can provide protection, but are not as effective as chlorothalonil for purple spot.

As lay-by season approaches, for your burndown consider that a survey last fall found no evidence of glyphosate or 2,4-D resistance in surveyed pigweed populations. Aim is also available as a burndown this year. It is a contact herbicide that acts similar to paraquat. With paraquat and other contact killers, consider that an immediate kill of tissue may reduce translocation of glyphosate into the plant, which would be most problematic with perennial weeds.

I have had interesting conversations with growers and consultants about common asparagus beetle over the last few weeks. Overall, carbaryl still appears to be providing control in most situations, though there have undoubtedly been fields where repeated applications have not provided complete control. These especially rough situations were in areas known to be hotspots. Over the past weeks, where problems have occurred growers have dealt with them by upping their carbaryl rate to full rate, spraying whole fields and not just edges, and trying Assail.

Another take-home from this year is the potential importance of timing. Beetle activity greatly decreases in cool weather, so applications made during cold spells may have less efficacy than those made on warm days. Overall, it appears that beetle pressure was simply high this year and problems were especially bad in fields that are typically hotspots, which are often bordered by pine trees (see photo).

For carrots, I captured aster leafhoppers in one field with a still-live cover crop, but did not catch any in another field this week.

For celery, 0 percent of leafhoppers tested positive for aster yellows for samples taken this past Monday, June 4, in Van Buren and Allegan counties. There was one sample from Allegan County taken May 31 with an infectivity of 6 percent. At this infectivity, the threshold for treatment is six leafhoppers per 100 sweeps.

For cole crops, diamondback moth and imported cabbageworm have been present in brassicas. Flea beetles are an annual problem in small-scale organic production. Floating row covers can be effective at excluding beetles, as long as the ground did not have brassicas last year. In the latter case, beetles may emerge under the row cover.

Entrust (active ingredient is spinosad) and Pyganic (acitive ingredient is pyrethrins) can be used for chemical control. For Pyganic, the pH of spray water should be between 5.5 and 7. More alkaline water can compromise efficacy. There are organic buffering agents that are very affordable. Add where needed as there is no sense wasting expensive organic insecticides!

For cucurbits, planting of butternut for processing has occurred and Jack O’ Lantern planting was ongoing at some Oceana County farms. The cucurbit downy mildew spore trap network is up and running. To date, spores have been captured in Muskegon and Saginaw counties, but not in numbers that are very concerning.

For peppers, my colleague noted that in southwest Michigan growers have observed that peppers planted in the heat prior to Memorial Day have not established well. Experience suggests stress during transplanting causes underperformance in peppers that no amount of “babying” can compensate for.

For potatoes, Colorado potato beetle adults have continued to be active. Planting of chip potatoes to our east in Montcalm County is continuing and behind normal pace.

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