Lygus bugs, moths present in sunflowers, keep your eye on stored grain

Manitoba Insect and Disease summary for August 10

Fusarium head blight in canary grass.


Insects: Insects of highest importance to scout for currently are Lygus bugs in canola and sunflowers, and banded sunflower moths in sunflowers. Only trace levels of soybean aphids have been found so far. There have still been no reports of high levels of larvae of bertha armyworms in Manitoba.

Plant Pathogens: Various diseases continue to be reported in field crops.

Disease Update

Canary grass: Fusarium head blight and root rot due to Fusarium spp was found in canary grass.

Peas: Pink seed of pea caused due to a bacterial pathogen, Erwinia rhapontici was reported in a field at low level. E. rhapontici is a bacterial pathogen that can cause yield and quality loss in peas. Fungicide application is not effective against this disease.

Corn: Goss’s wilt is being found in fields with multiple years of corn and less tolerant hybrids. For more information on Goss’s Wilt, visit the Manitoba Agriculture website.

Insects on sunflower heads

Lygus bugs and banded sunflower moth are present in sunflowers and in some fields presence of sunflower seed maggots has been noted. There have been no reports of high levels of sunflower seed weevils in Manitoba.

When does it become too late to manage Lygus bugs in sunflowers? In research trials in North Dakota, damage to sunflower heads by Lygus bugs was approximately twice as severe when feeding occurred at late bud and early bloom compared to stages when heads had completed flowering. At these earlier stages, the feeding will injure the kernels and the destruction of the cells will result in the characteristic depressions and browning of the kernel. If adult densities reach the economic threshold, lygus bug management should be initiated prior to or at the beginning of the bloom stage.
When flowering has finished (by R6) the seeds are probably too mature to sustain damage any longer.

Also consider that in flowering sunflowers there will be pollinators, which are also helping improve yield of the sunflowers, as well as providing a livelihood for beekeepers. The only insecticides registered for Lygus bugs in sunflowers are Matador and Voliam Xpress, which can not be applied to flowering crops when bees are visiting the treated area. Both labels also state “spray deposits should be dry before bees commence foraging in treated crop”. So if treatment is necessary for Lygus bugs in sunflowers, spraying as late in the day as practical is preferred.

Pupal cases on sunflower heads: This time of year you may find small brown pupal cases on the heads of some sunflower plants. These are the pupae of an insect called the sunflower seed maggot (Neotephritis finalis). Larvae feed on the florets and the first generation pupates in the head. They are generally considered to be not economical to sunflower seed production, however studies on the economics of this insect are being conducted in North Dakota.

Insects in stored grain

Preventing stored grain insects: A reminder before moving and storing new grain to clean old grain out of bins, augers, combines, truck beds, and other areas where grain or grain debris may be. Infestations of stored grain insects such as rusty grain beetles usually do not get started by harvesting the insects along with the grain. They are often the result of insects already being present in bins or equipment used to move grain, or insects being able to get into the stored grain through openings in bins or storage structures. Some insects in stored grain, such as the rusty grain beetle, will feed primarily on the grain, while others, such as foreign grain beetle, may be feeding primarily on moulds growing on grain that is too moist. So it is good to know the species you are dealing with as management options may differ. Additional information on identifying and managing insects on stored grain can be found on the Manitoba Agriculture website.

For long-term storage of grain, lowering the grain temperature below 15 C as soon as possible after the grain is placed in storage can help minimize the risk of stored grain insects. Below 15 C potential insect pests of stored grain stop laying eggs and development stops. Grain that is not aerated or moved after harvest can often remain warm enough for insects to survive the winter.

To read the full Manitoba Insect & Disease Update for August 3, complete with current insect monitoring programs and trap counts, click here.

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