West central Michigan vegetable update - June 26, 2019
Finally, some good weather for growing! Unfortunately, it’s also good weather for disease development.
Asparagus harvest is coming to a close in west central Michigan. Make sure to cover ferned out, younger fields with chlorothalonil, preferable to mancozeb under current conditions, given weather has been good for purple spot development. Phytophthora symptoms have been reported by multiple growers and industry members. This is not a surprise given the wet weather, both late last summer and this spring. Symptoms of spear infections include water soaking where infested soil has splashed onto spears. Crowns can also be infected, leading to spears that emerge and die. Learn more about Phytophthora in asparagus.
For carrots, an aster leafhopper sample taken from Oceana County on June 21 had 0% infectivity.
Celery has reportedly been growing well in the cool weather where it could be planted, with lots of “hopscotching” around as growers seek dry ground to plant. The herbicide Zidua is now labeled for celery (See Zidua now labeled for use in 2019). This is a pre-emergence herbicide to be applied within six days of transplanting. It provides control of purslane and some other problem weeds. Winged aphids have been present in some fields, but colonies have not been detected. Overall, scouts report leafhopper numbers have been very low. However, symptoms of aster yellows were observed in celery; this occurred in the county that had our single positive for aster yellows.
For cole crops, diamondback moth caterpillars have continued to be present in an Ottawa and Kent County locations MSU interns are scouting. Note, in other crops, onion thrips have been present.
Onions need to be protected with fungicides given the weather. Mary Hausbeck suggested tailoring programs for Stemphyllium (which is a persistent problem) while keeping an eye out for downy mildew, which we have also had favorable weather for. Since we know Stemphylium is a recurring problem, Mary recommends using chlorothalonil in place of mancozeb right now. In Stemphylium trials, mancozeb was not effective, but chlorothalonil did help prevent Stemphylium.
This creates a conflict with thrips control objectives, as chlorothalonil and Movento are not good tank mix partners. Overall, given the weather, consider giving disease control a priority over the next week. Onion thrips were present at low levels yesterday in a Newaygo and Kent County field I scouted, with 12% of plants having thrips at both locations, but populations were less than 0.25 per leaf. In New York State, Cornell University partnered with growers who only treated fields once thrips reached 0.6-1 per leaf, and showed no yield reduction while documenting savings on their spray programs. The 0.6 thrips per leaf threshold is to allow for lag time between scouting and insecticide application. Remember to use a surfactant with Movento and avoid tank-mixing it with Bravo. Effective surfactants could include organosilicone surfactants, methylated seed oils (MSOs) and non-ionic surfactants. Given the disease weather, it is worth considering making separate Movento and chlorothalonil applications if possible.
For root crops, Cercospora and Alternaria have been detected in sugar beets in eastern Michigan. Given the weather, protecting beets with foliar fungicides makes sense.
For tomatoes, peppers and potatoes, early blight symptoms have developed in southwest Michigan. Consider applying chlorothalonil as a protectant spray on a seven to ten day schedule. Bacterial leaf spot has also been detected in peppers. Late blight has not yet been detected in the Great Lakes region.