2014 Highlights: UC IPM Annual Report
Management of Destructive Crucifer Pest
Damage to cabbage plants. Cabbage maggots feed on plant roots, resulting in yellowing and stunted growth. (Photo by S. Joseph)
IN BRIEF
- IPM programs developed for cabbage maggot in other states do not work well in California due to milder winter weather.
- Reduced-risk pesticides can prevent cabbage maggot damage with precise application timing when maggots are small.
- Joseph?s research suggests the optimum timing is several weeks after planting.
Cabbage maggot is a destructive pest of cruciferous crops—broccoli, cauliflower, cabbage, broccoli raab, and Brussels sprout—that are worth $1 billion in California. Maggots feed underground and cause plants to yellow, have slow growth, and become stunted. In other regions where cabbage maggot is a problem, IPM programs have been developed. Unfortunately, California’s mild weather is different from other regions where cabbage maggot is a problem. Because it rarely freezes along the coast, cabbage maggot remains active over the winter so previously developed IPM programs in other states do not work in California.
Without an IPM program, cabbage maggot management consisted of the persistent use of soil-applied organophosphate insecticides. This was not a viable long-term management strategy. High concentrations of these insecticides were found in nearby water bodies. Organophosphate resistance developed. In 2008, state restrictions on organophosphate insecticide use left growers with fewer options to manage cabbage maggot. The result was widespread crop losses.
UC IPM Advisor Shimat Joseph, with Jesus Martinez from Hartnell College, studied the cabbage maggot along the California central coast with the overall goal to develop an IPM program. Most current insecticide options for cabbage maggot are reduced-risk and less persistent. This is good for the environment and human health but requires precise timing in order to be the most effective at preventing crop damage. Joseph’s research identified that precise timing when the crop is most susceptible to cabbage maggot.
Joseph’s research showed that injury from cabbage maggot did not appear until several weeks after planting. In fact, very few eggs were observed on broccoli and turnip seedlings just after planting, even though cabbage maggot adults were in the fields. This is important because insecticides for cabbage maggot are typically applied at planting. Joseph’s results show that applying insecticides at this time may be less effective at preventing crop damage.
Joseph suggests applying insecticides three to four weeks after planting seeds. Reduced-risk pesticides are less persistent and have shorter residual effects. Waiting to apply several weeks after planting takes advantage of when the crop needs the most protection; and during this time maggots are small, which is when cabbage maggot is most vulnerable to insecticides.
It is anticipated that Joseph’s research will result in a more precise application timing of reduced-risk insecticides, leading to better control of cabbage maggot, and resulting in reduced crop losses. His work will contribute to the successful use of reduced-risk pesticides and that may lead to less use of organophosphate insecticides, which have been shown to contaminate water bodies near where cruciferous crops are grown. Research continues to investigate thresholds and different management techniques (cultural, biological, and host-plant mediated) toward the development of a more comprehensive IPM program.
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