Regional reports on Michigan vegetables – August 17, 2011
MSU Extension educators’ pest and vegetable updates for Michigan.
This week’s regional reports:
- Southwest Michigan – Ron Goldy
- East Michigan (Lapeer, Macomb, St. Clair) – Hannah Stevens
- Grand Rapids Area – Bill Steenwyk
- West Central Michigan – Norm Myers
Southwest Michigan – Ron Goldy, Michigan State University Extension
Temperatures averaged slightly below normal with highs from 73 to 82°F and lows from 54 to 61°F. The area received a trace to over 2 inches of rain depending on location. Most precipitation occurred on August 13.
The biggest story continues to be the weather. Season-long rainfall has encouraged disease development. Frequent storms have encouraged disease development and storms with heavy down pours and strong winds have caused spread within and between plantings. This is especially true for bacterial diseases evident in Solonaceous and cucurbit crops. Fields that looked good last week show severe symptoms this week.
Watermelon and fall squash harvest has begun. Powdery mildew is evident in pumpkin and squash fields. Pumpkins are sizing well since there is adequate soil moisture and heat. No sign of squash bugs and virus symptoms continue at a low level. No additional reports of downy mildew, but it is in the area so growers need to make protective fungicide applications.
Bacterial problems are evident in most tomato fields. Harvest from early tomato fields is finished. In some cases, it was hurried by severe bacterial disease infection. Bacterial spot continues to be evident in pepper fields.
European corn borer numbers remain low being at “0” for this week.
Two more rain events in the past week, including a heavy but brief downpour on Saturday evening, August 13, have added a little too much mud to harvest operations. Yesterday, August 16, was the warmest of the week, reaching a high of 85°F with a maximum on Sunday, August 14, of 71°F.
In sweet corn, European trap catches remain low but steady and the corn earworm trap was empty as was the western bean cutworm trap. Early tomatoes are now being harvested in quantity and fields are cleaner in terms of disease than I have seen in a long time.
Tobacco hornworms may be found in tomatoes and have been reported on peppers where insecticide use has been minimal, but these larvae are also parasitized by a number of insects. One of the most common is a small parasitic wasp. Larvae that hatch from wasp eggs laid on the hornworm feed on the inside of the hornworm until the wasp is ready to pupate. The cocoons appear as white projections protruding from the hornworm’s body (Photo 1). If such projections are observed, the hornworms should be left if possible as they are essentially already dead and leaving them will conserve the beneficial parasitoids. The wasps will destroy the hornworms when they emerge from the cocoons and will seek out other hornworms to parasitize.
Photo 1. Parasitized hornworm.
In cucurbits, pumpkins and winter squash are beginning to show some color and some will be on the wholesale market soon. Growers are moving into successive plantings of cucumbers and pickles and downy mildew is not uncommon. Pytophthora capsici is taking down susceptible crops such as peppers in isolated areas, but pepper harvest is well underway (Photo 2). Carrot harvest is in full swing.
Photo 2. Phytophthora capsici on peppers.
The weather was a bit cooler and less humid last week, with highs mostly from 75 to 83°F. Significant rain fell Saturday, August 13, with many areas receiving 1 to 2.5 inches.
Sweet corn harvest continues at a brisk pace with reports being generally positive. European corn borers are present, but not at severe levels. European corn borer moth trap counts in southern Kent County were 4, 5 and 0 for the three traps. Reports from tomato growers vary from very good to fair. Peppers are, with some exceptions, looking good.
Cabbage harvest is nearly half complete. Reports are mostly positive, although some loss from bacterial rot and thrips is evident.
Zucchini harvest continues with good quantity and quality. Winter squash harvest is underway and 5 to 10 percent complete. Yields are fairly good. Some powdery mildew and Phytophthora blight is present. The melon harvest has been favorable.
The root crops, including red beets, turnips and parsnips, are being harvested with good overall results. Wet soils in some areas are preventing new plantings.
Tomato, pepper and eggplant harvest is underway, with fairly good results. Tomato yields were reduced in some of the wetter areas.
A small fraction of the onion crop has been harvested. Many growers have rolled the tops of mature stands and will soon begin harvesting. Damage from thrips remains light to moderate. Most frequently mentioned disease challenges include purple blotch, Stemphyllium leaf blight and bacterial soft rot.
Celery harvest is approaching 50 percent. Yields and stalk size had been somewhat lower in areas that had received heavy rainfall followed by high temperatures in July. The current crop is yielding somewhat better. Professional field scout reports indicate low numbers of aster leafhoppers and declining populations of variegated cutworm. Aphid pressures require constant attention from growers. Early blight has been the major foliar disease issue. Celery anthracnose can be found at low levels in many fields.
All of Oceana County got significant rain on Friday night (August 12) and Saturday morning (August 13), with amounts ranging from 1 to 2.25 inches. That rain has given all of our irrigators a break this week.
In asparagus, serious defoliation from purple spot is showing up now in fields where disease programs were not up to snuff. Rust is still pretty much under control in most areas. Some growers will begin to spread rye cover crops into asparagus with the next fungicide application. Asparagus growers have also been paying attention to MSU horticulturist Mathieu Ngouajio’s brassica cover crop work and a significant acreage that is going into asparagus next year is being planted to mustards of one variety or another.
Disease pressure remains high in vine crops. Not only is powdery mildew a concern, but Phytophthora capsici has also made its appearance in processing and Jack O’Lantern pumpkins and I am sure this weekend’s rains will only make the situation worse. Watermelon mosaic virus continues to be a problem for zucchini growers, but so far is only of concern in yellow varieties. Cucumber growers report downy mildew present, but under control. Fruit set on all vine crops has been very erratic this year and no one, including me, can figure out just why. Some fields have yielded steadily, while others will have week-long gaps where almost nothing is picked.
In carrots, disease pressure has abated a little bit due to the cool nights, but with a return of warmer weather we will probably be back in a high-pressure situation. Our local aster yellows index increased a little bit, but is still low for this time of year at 25 per 100 sweeps.
I caught one European corn borer moth, but my corn earworm moth catch dropped to two this week. Western bean cutworm numbers have dropped off greatly this week, with no moths caught in my sweet corn site and only three in my field corn site.
I would like to mention that our Oceana Research Tour is scheduled for Tuesday, September 6 from 1:00 to 5:00 p.m. Agendas and maps are available from my office. This year’s tour features MSU research plots for both asparagus and carrots.