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BURLEY, Idaho — A procession of insects can infest sugar beets throughout the growing season, and knowing which might hit, and when, can give growers a leg up on controlling them.
Plants are most susceptible to damage early in the season when seedlings are small, Erik Wenninger, an entomologist at the University of Idaho, told growers during the Snake River Sugar Beet Conference.
Sugar beets can tolerate a good amount of foliar damage later in the season, but they’re highly susceptible to insects in April and May, he said.
In a seasonal timeline of insects, wireworms and cutworms are the primary threat to seedlings, he said.
Wireworms favor cool, wet springs and typically feed on plants early in the season. They feed on the roots and cause damage that can kill seedlings and reduce stands, and they can have a five-year lifespan in the soil, he said.
Cutworms are the larvae of night-flying moths, and there are lots of species. They can cause a lot of damage, killing seedlings and reducing stands, he said.
Beet leafminers are next in line. They seem to be appearing earlier than they used to, showing up in mid-May. They reduce photosynthesis and with a high enough population can kill seedlings, he said.
The sugar beet root maggot typically shows up in the area in May. It cuts through the root of the seedling in the early season and causes scarring on the root in mid-season. It stops feeding in July, he said.
Lygus bugs are a mid-season pest, preferring hot, dry weather. Similar to aphids, they suck sap from the plant that causes distortion and discoloration and leads to necrosis. They appear sporadically in potatoes and feed on seed crops, he said.
The beet leafhopper is a similar mid-season pest, sucking sap from the plant. It doesn’t cause a lot of direct damage, but it transmits the beet curly top virus. It’s usually seen mid-May to mid-July, but the timing of its appearance depends on weather, he said.
Dryness in the desert, where the insect overwinters, causes it to move to new host plants, he said.
“So timing in sugar beets varies. The earlier the infection, the more severe the symptoms,” he said.
Webworms and loopers are next, typically seen in mid to late season. The larvae are similar to caterpillars and cause defoliation damage, he said.
Spider mites infect sugar beets about the same time. They cause stippling and bronzing of leaves that reduce photosynthesis, he said.
“They feed on just about any crop in Idaho and weeds as well,” he said.
Rounding out the season are the sap-sucking bean aphid and sugar beet root aphid. The bean aphid shows up about mid-July. It causes curling and yellowing and produces honeydew, which causes a sooty mold on leaves, he said.
“It’s much more of a concern if it’s carrying a beet virus,” he said.
The root aphid feeds on the roots, which limits water and nutrient uptake, affecting yield. It’s very much a late-season pest, showing up in late July or early August, he said.
“Basically, we have insects attacking sugar beets throughout the season,” he said.
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December 18, 2019 at 12:04PM