West central Michigan vegetable update – Aug. 15, 2018
A recent trial revealed clear differences in product efficacy for controlling Stemphylium in onions. Sweet corn growers should be on the lookout for earworm.
Based on Oceana County TomCast sensors in asparagus, a fungicide application would have been due Monday, Aug. 13, if fields where sensors were located had not been sprayed since around Aug. 1-4. Be on the lookout for European asparagus aphid. This pest is not a problem most years, but when it does occur it can cause damage. See “Check your asparagus field for aphids” from Michigan State University Extension for more information on European asparagus aphid and product efficacy.
Disease symptoms in carrots continue to be present. If you are using the strobilurins Cabrio or Quadris, consider tank-mixing a protectant such as chlorothalonil with them. As we move through the season, remember that Merivon and Luna Tranquility are newer materials that can be considered during periods especially favorable for foliar disease.
Twospotted spider mites were causing damage at two celery farms I visited in the past week. Abamectin (e.g., Agri-Mek, seven-day pre-harvest interval) was being applied. If you are looking for alternatives, Oberon is labelled via a Special Local Needs label for celery (seven-day pre-harvest interval). Scouts report aphids continue to be present. Movento (three-day pre-harvest interval) applied with a penetrating surfactant can provide control.
In cole crops, imported cabbage worm and diamondback moth larvae have been present in organic fields. Bt products can provide control of these pests for organic growers.
In cucurbits, cucurbit downy mildew has been on the move in west Michigan.
Harvest of early maturing, sown onions had or was starting over the past week. Trials conducted by MSU’s Mary Hausbeck highlighted that, of the tested products, the Luna products (Luna Experience or Tranquility) are most effective for Stemphylium. Of the protectants, chlorothalonil provided significantly more protection from Stemphylium than did mancozeb. Consultants reported seeing some anthracnose and downy mildew, but this has not been widespread.
For potatoes and tomatoes, late blight has been confirmed in Wisconsin and Illinois. Watch for reports out of Michigan in the next few days.
Corn earworm captures in sweet corn increased starting about Aug. 6 at an Oceana County location, and a colleague has also reported an increase in captures in southeast Michigan. The size of your trap catch can help you determine your spray interval (Learn more at “Video tutorials on using pheromone traps to monitor corn ear worm in sweet corn” from MSU Extension.).
Of the pyrethroids, research at Ohio State University suggests Hero is most effective. For conventional growers, Radiant, Coragen and Besiege (a tank-mix of the actives in Coragen and Warrior) provide alternatives to pyrethroids. Experience at Ohio State over a decade suggests that in low-pressure years, pyrethroids can still provide control, but under high pressure, alternatives can provide improved protection. Spray intervals during earworm season can be between two and five days, with tighter intervals during high captures or hot weather.
My colleague has noted western bean cutworm larvae were abundant in her field trial. This pest is different than corn earworm in that you can find multiple larvae per ear (earworm larvae are cannibals and only the “hungriest” survive). Western bean cutworm has a single generation each year. Corn that was just about to tassel in the last few weeks would be most at risk.