Monthly Archives: June 2012

Beware of Blackleg

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As the season progresses and as conditions stay cool and damp the possibility for Blackleg to appear in canola is greater. Blackleg (Leptosphaeria maculans) is a fungus that can cause significant damage and yield reduction to a canola crop under the proper conditions. Blackleg is a fungus that can come from infected seed or from spores created by old infected canola stubble residue. There are two types of strains mildly virulent and highly virulent which can infect canola crops. The mildly virulent strain will cause minimal damage and minimal yield loss. The highly virulent strain can cause significant damage and yield loss. Blackleg can infect canola plants as early as the cotyledon stage up to the early maturing stage of the plant. While it is extremely difficult to spot at the early onset of infection, grayish white legions can appear on stems or leaves with tiny pepper like black spots or spores, called pycnidia which can be spread by wind or rain to neighboring plants and infect them as well. It is recommended that farmers use preventative maintenance to avoid blackleg infections in their canola crops. Some of the tools to prevent Blackleg infection in your crop would be to:

First: select Blackleg resistant varieties which will be the best way to prevent the disease in your fields.

Second: is rotation. Canola crops grown back to back or in very short rotations are more susceptible to infection.

Third: is to use fungicides to treat crops that may be susceptible to the disease.

On some of our scouting trip this summer we have found Blackleg spores growing on old canola stubble below the crop canopy. The cool wet conditions are ideal for the growth of the spores. Some spores can travel several kilometers in the wind so beware of neighboring fields that had canola in their rotation in previous years. It is important to scout fields around the time of swathing to identify if black leg has indeed infected your crop. By doing this it can help farmers make decisions to prevent the disease in future crop years. If you think you may have the potential to have blackleg infections in your canola crop, please speak to your chemical reps about possible fungicide applications. Some registered fungicides have staging and pre harvest restrictions as well as export restrictions on harvested grain treated with certain fungicides.

As the growing season progresses and the country side turns yellow we invite producers to keep scouting fields and look for possible disease issues or insect pressure. Stay tuned for more information on other diseases and insect information. Enjoy your summer and happy farming.

Ramblings from Dan.

 

Cereal Leaf Beetle

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Description

Cereal leaf beetle adults are about 3⁄16 inch long and 1⁄16 inch wide. The adults have dark, metallic blue wing covers, orange legs, and an orange collar. The head and the rest of the body are black.

Eggs are cylindrical with rounded edge. They are light orange when laid and darken gradually over time to almost black. Eggs are deposited singly or in rows of two to four on the topside of the leaves.

Each female lays from 12 to 50 eggs.

Cereal leaf beetle larvae are pale yellow with a brown head and legs. In the field, they look mostly black because they smear excrement over their bodies. People walking through a field infested with cereal leaf beetle larvae may emerge with black stained pants legs because this black coating easily rubs off the larvae. The larvae are about 1⁄16 inch long just after hatching and 1⁄4 inch long when fully grown.

Damage

Cereal leaf beetle larvae feed on the leaves. Feeding activity results in long, window like slits in the leaf blade. When feeding is severe, the entire leaf becomes brown and ragged. Cereal leaf beetle larvae are especially damaging when they feed on the flag leaf and when large numbers of larvae are found before head emergence.

Life Cycle

The cereal leaf beetle has one generation per year. Adult beetles spend the winter in the woods and field borders. During the first warm days of spring, the beetles disperse into small grain fields, mate, and begin to lay eggs. Eggs hatch in about 7 days, and larvae (immatures) begin to feed on the cereal leaves. Larvae are usually first found after flag leaf emergence but before the heads have emerged. The larvae feed for about 3 to 4 weeks, then leave the plant, and move down into the soil.

Control

Check fields weekly for about a month. Check the middle of the field as well as the edges. One way to check fields is to walk back and forth in the field in a zigzag pattern. Look for feeding damage, adult beetles, eggs, and larvae. Stop in five to ten areas in each field, and count eggs and larvae on the top two leaves of five stems. If cereal leaf beetle larvae have begun to hatch and there is more than one cereal leaf beetle egg or larva per two stems, treat with one of the suggested insecticides. All suggested insecticides provide good control of cereal leaf beetle larvae. Because dying larvae are hard to distinguish from living ones, wait 2 to 3 days after treatment before checking to make sure the treatment was successful.

Other Management Strategies

Beetles prefer thin stands so follow good agronomic practices that promote full stands and high-yielding wheat. Also avoid late planting because adult beetles typically prefer less mature plants to more mature plants. Heavy rains can kill immature cereal leaf beetles. If heavy rains occur between the time a field is checked and insecticides are to be applied, wait for the foliage to dry and check the fields again. Cereal leaf beetles are controlled by natural enemies. Eventually, this and other natural enemies will help keep cereal leaf beetle populations below economically damaging levels. Ladybird beetles are also important predators and can destroy many eggs and larvae.