Southeast Michigan Vegetable Update – June 5, 2019

More insects are becoming active, though field activity is still limited.

Two species of ladybeetle out on aphid patrol
Two species of ladybeetle out on aphid patrol. Photo by Marissa Schuh, MSU Extension.

Weather

Last week brought 2 to 3 inches of rain to the southern portions of our region, as well as a band of hail-producing severe weather. Looking ahead, a high pressure system is entering our area, bringing warmer temperatures and hopefully less rain.

The table below shows rainfall totals for the MSU Enviroweather stations in southeast Michigan, as well as degree-days calculated using the Baskerville-Emin Method. Degree-day average for Commerce and Hudson is over five years, while Deerfield is over two years. Rainfall is in inches, with number in parenthesis indicating rainfall since the last report. For a refresher on degree-days and how to get this information in your area, see “Accessing growing degree days with Enviro-weather” from MSU Extension.

Rainfall and Degree Day Totals as of June 5th

Station

Degree Days (Base 42)

Degree Days (Base 50)

5-Year Degree Day Average (Base 50)

Rainfall since April 1st

Commerce

720

356

488

8.34 (+0.96)

Deerfield

856

444

605.7

10.67 (+2.18)

Hudson

775

397

536.1

9.71 (+2.13)

Crop reports

As asparagus harvest wraps up, remember that after the last harvest is a key window for weed control. A clean pick followed by a glyphosate application is very effective. For more information and options, see Bernie Zandstra’s article “Watch the timing for post-harvest weed control in asparagus.”

Basil downy mildew is causing issues in some Michigan greenhouses. This disease starts with the seed. For conventional greenhouses, both Subdue Maxx and Ranman have labels and are effective in controlling basil downy mildew. Organic control is more challenging, and the best course of action is to be vigilant and rogue aggressively.

Cole crop caterpillars are out, but I haven’t been in a conventional or organic field that is at the threshold for diamondback moth or imported cabbageworm. On organic farms, there are low levels of aphids out and increasing flea beetle activity. Cabbage maggot larvae damage is becoming apparent. Peak flight of adult cabbage maggots is over in most of our region, meaning while there may still be some stragglers laying eggs, peak egg laying has passed.

It has been too wet to spray, and ladybeetle adults, larvae, and eggs can be easily found in many fields. Eggs are bright yellow, oblong and laid in clusters. These beneficial insects help manage pests like aphids, and can be preserved by using selective insecticides, like Bt for small caterpillars or Coragen.

Table 1. Thresholds for the three caterpillar pests of cole crops.


Crop


Stage

% Infested

Diamondback Moth Larvae

Imported Cabbageworm and Cabbage Looper

Cabbage – Fresh

seedbed

not applicable

not applicable

transplant to cupping

50% with ≥ 5 larvae/plant

30%

cupping to early head

50% with ≥ 5 larvae/plant

20%

early head to harvest

10% with ≥ 1 larva/plant

10%

Broccoli, Cauliflower

seedbed

10%

10%

transplant to first curd

40%

20%

first curd to harvest

10%

10%

Cabbage edema
Edema scars on the underside of a cabbage leaf, the upper side only displayed minor yellow discoloration. Photo by Marissa Schuh, MSU Extension.

Another thing I’ve seen in cole crops is edema (or oedema). This is a disorder I often see in pumpkins, but it can also be found in cole crops. When conditions are wet and cool, leaves take up water faster than they lose it through transpiration, causing cells to swell and burst. The burst cells then scar over, giving leaves a crusty appearance, almost like that of a peanut shell. It is most often seen on the underside of leaves, and is something leaves do not grow out of. Once things warm up and dry out, these symptoms should stop appearing.

Garlic plants are getting ready to produce scapes.

For peppers and sweet corn, the first generation of European corn borer is out. This generation typically does not cause damage to these crops, but how well this generation does will determine how much damage we see from the second generation. There isn’t a lot of field corn planted and what is out is pretty small. European corn borer larvae need non-bt corn plants 8 inches or taller to feed. Unfortunately, this pest has a large host range, so they will find something to eat in the landscape.

As adverse weather conditions persist, transplants are being held longer. Look out for botrytis, likely to be our biggest disease issue with the current weather. Humidity management to reduce leaf wetness is key in control.

In vine crops, both striped and spotted cucumber beetles have been found in our region. Striped cucumber beetles live here year round, so the beetles we’re seeing now are those that spent the winter hunkered down in field debris and wooded areas. Spotted cucumber beetles are typically not seen until later in the year, and are carried here by storms from the south. With all our southern-origin, low-pressure systems this year, it is likely the beetles rode one of these to our area. Direct-seeded crops with an insecticide seed treatment have early season protection, but transplanted crops likely don’t have any activity left from seed treatments. The threshold for these beetles is one adult per plant on seedlings, and five adults per plant on mature plants.

If you are worried about bacterial diseases, such as angular leaf spot, remember that these diseases can be seedborne, meaning copper applications need to start early and stay routine. Copper should be applied every 7 days from first true leaves onward. Be careful with timing copper applications. When these formulas sit on the leaf they can cause phytotoxicity.

Meetings

  • Tomorrow, June 6, from 3-5 p.m. MSUE fruit educator Bob Tritten is hosting a meeting on strawberry insect and disease management. The meeting will be held in Ida, is free, and no registration is required. For the full info, see “Attend the statewide pre-harvest strawberry meeting on June 6.”
  • Mark your calendar! The 2019 Great Lakes Fruit, Vegetable, and Farm Market EXPO is scheduled for December 10-12th in Grand Rapids, MI.

Reach out

Contact me at schuhmar@msu.edu or at 517-264-5309 to schedule a farm visit or ask a question.


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