West central Michigan vegetable regional report - August 6, 2014
Late season diseases could still pose significant challenges to vegetable growers in what has proven to be more of a disease than insect year.
August 6, 2014 - Author: Ben Werling, Michigan State University Extension
Michigan State University Extension specialist Zsofia Szendrei reported today, Aug. 6, that asparagus miner adults of the second generation are now active and laying eggs. Now is a good time for growers who consider foliar insecticides a good control option for this pest to make an application. Use the MSU Enviro-weather website to track asparagus miner development.
Remember that even though rain has been sparse in our asparagus growing region, morning dews are as good as rain at promoting development of asparagus purple spot. There is still time left in the growing season for this disease to impact asparagus, so growers should continue to apply protectants according to disease weather models.
Black rot was an issue at one Ottawa County location this year, and in general is a major challenge to cole crop growers. This disease can be seedborne and can also persist on undecayed plant debris in the field. Currently, the best option for control of this pathogen on susceptible varieties is weekly applications of a fungicidal/bactericidal copper, starting in the transplant greenhouse when applicable. Note that fertilizer grade copper can have much too low a copper concentration and is not useful as a preventive for this or other diseases. Cabbage and broccoli varieties are available with resistance to this pathogen.
Aphids were of concern to some area celery growers this week. Movento (active ingredient spirotetramat) is a very effective product when combined with a penetrating surfactant. See pages 6-7 of “Michigan Vegetable Insecticide Evaluation Studies 2013” to access Szendrei’s evaluation of surfactants.
To stay abreast of cucurbit downy mildew, access Mary Hausbeck's website at veggies.msu.edu which maintains a network of spore traps for cucurbit downy mildew – useful in predicting how much inoculum is available to spread to other regions – plus information on spray programs. The cucurbit downy mildew forecaster suggests low to high risk of spread of cucurbit downy mildew into west Michigan early this week. Reports of powdery mildew on cucurbits continued today, with first observations occurring on lower leaves.
Diseases continue to be the main concern this year with some isolated increases in thrips populations, but no major problems being reported. Growers should continue to use products that prevent problems with onion downy mildew given this year’s weather.
Potatoes and tomatoes
Late blight has been confirmed from 25 potato fields in Montcalm County to our east, and symptoms consistent with this disease were present and severe in an Ottawa County tomato field yesterday, Aug. 5. For tomatoes, preventive sprays of relatively cheap fungicides on a seven-day schedule, including products such as mancozeb, Bravo (active ingredient chlorothalonil) and Quadris (active ingredient azoxystrobin), can help ensure you have a harvestable crop.
Growers who abandon blighted plantings can kill plant tissue using glyphosate, which will help stop spread to other area growers. If you use mechanical means to kill blighted plantings, be sure you clean equipment well to avoid spreading it to other tomato or potato plantings. Forecast risk is high for development for two to four out of the next five days at most west Michigan locations through Sunday, Aug. 10, according to www.lateblight.org.
Overall, western bean cutworm populations to our west in Montcalm County have been low this year. I captured western bean cutworm moths again this week at an Ottawa County location. Females of this pest prefer to lay eggs on corn that is just about to tassel on the upper surface of the top four leaves. I did not detect any egg masses today at the location where this pest was trapped. Larvae initially feed in the whorl, but move to ears upon tasseling.
Unlike corn earworm, which are cannibalistic and eat each other until only one worm remains in an ear, multiple western bean cutworm larvae can coexist, with larvae moving from the silks and boring into the side of the ear if silks are occupied by their siblings.