Articles for May 2015


From the May 21st NDSU Crop and Pest Report:

During the middle of May 2015, early morning frost occurred in many parts of North Dakota. The temperature at which freezing injury may take place in canola varies with the growth stage of the plant, soil moisture content, and the length of time the temperature is below freezing. Early seeded canola, after several days of near freezing temperatures, may undergo a gradual hardening process that will allow the plants to withstand freezing temperatures without serious damage.

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Frost Tolerance of Spring Seeded Canola

Frost can occur in any month; however, frost occurring in the spring and late August or early September can be critical. The temperature at which freezing injury occurs varies with the plant’s stage of growth, soil moisture content and the length of time the temperature remains below freezing. Damage occurs when ice crystals form within the plant or the plant actually freezes, causing cell walls to rupture. A severe drop in temperature that lasts only a very short time may not damage canola plants, while a light frost of a several degrees below freezing that lasts all night may cause severe damage. The amount of frost injury will depend on soil moisture conditions, the rate at which thawing occurs, the growth stage of the plants and the amount of cold temperature hardening the plant is exposed to prior to freezing temperatures.

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Aster leafhoppers and other species of leafhoppers were observed in large numbers in a winter wheat field near Aneta in Nelson County (source: Huso Crop Consulting). Aster leafhopper (Macrosteles quadrilineatus) and an unknown leafhopper (possibly a Chlorotettix species) were collected from fields by Leslie Lubenow. Both species of leafhoppers are known to vector aster yellows, although Chlorotettix species are not documented to feed on wheat. Most aster leafhoppers migrate into North Dakota on southerly wind fronts. Aster leafhoppers are small (1/8 of an inch), wedge-shaped and green to yellow with three pairs of spots on its head. Leafhoppers are active and mobile insects. These leafhoppers feed on plant sap and vector aster yellows, a phytoplasma disease.
As reported in the past issues of Crop & Pest Report, there is little research information on pest management of aster leafhoppers to minimize vectoring of aster yellows. So, it’s a good idea to scout fields regularly for influxes of large populations of aster leafhoppers. This pest has caused economic yield loss in wheat and canola in the past in North Dakota, especially in 2012.
Aster yellows is caused by a phytoplasma, an organism similar to a bacterium but without cell walls. Symptoms of aster yellows in wheat are similar to Barley Yellow Dwarf Virus (BYDV). Aster yellows can cause yield loss in susceptible wheat varieties when infections are high. Plants are more susceptible to aster yellows during early growth stages. There is no economic threshold that has been developed for aster leafhopper in wheat or canola. However, you need both high densities of aster leafhoppers and high incidence of aster yellows being vectored by leafhoppers to cause significant yield losses.
Story submitted by Jan Knodel NDSU Crop & Pest Report.

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