Articles for May 2015

CANOLA AND FROST DAMAGE

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.

Frost damage occurs to the small canola plant when ice crystals form within the leaf or stem tissue or when the plant actually freezes, which will cause cell walls to rupture. A severe drop in temperature which only lasts a very short time, may not damage canola plants; while a light frost of several degrees below freezing that lasts all night may cause severe damage.

Canola seedlings will usually recover from a light spring frost that does not damage the growing point of the plant. If a heavy frost does blacken the leaves, no action should be taken for at least 4 to 7 days. The extent of injury can be determined in a week or less following the frost. If there is any green color at the growing point in the center of the frozen leaf rosette, the plant will recover and yields will most likely be higher than if the field is re-seeded.

In evaluating frosted seedling fields, consider the percentage of plants killed and the percentage recovered. The surviving plants should be evenly distributed in a field. Even if two-thirds of the seedlings in a reasonable stand are frost killed, the field will usually produce more when left than if re-seeded. The surviving plants will take advantage of the reduced competition for light, moisture and nutrients, and grow larger, producing more branches, pods and seeds per pod, thereby compensating for the lost plants. The surviving plants may require five to eight days longer to mature; but a re-seeded crop will require an even longer period to reach maturity.

Story by: Hans Kandel – Extension Agronomist Broadleaf Crops

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.

Canola seedlings usually will recover from a light spring frost that does not damage the growing point of the plant. If a heavy frost does blacken the leaves, take no action for at least four to seven days.79 The extent of the injury can be determined in a week or less following the frost. If you see any green at the growing point in the center of the frozen leaf rosette, the plant will recover and yields will be higher than if the field is torn up, reworked and reseeded. Early seeded canola, after several days of near-freezing temperatures, will undergo a gradual hardening process that will allow the plants to withstand freezing temperatures without serious damage. A number of chemical changes occur, resulting in a higher concentration of soluble substances in the cell sap. Research in Canada has shown that early seeded canola that had undergone hardening could withstand 18 to 20 F temperatures, while later-sown canola that did not undergo hardening was killed by temperatures of 25 to 26 F. In North Dakota, canola seedlings have withstood temperatures as low as 22 to 23 F with only limited frost damage or stand reduction. In evaluating frosted seedling fields, one must consider the percentage of plants killed, the percentage recovered and the time of year. The surviving plants also should be somewhat evenly distributed in a field when allowing the stand to remain for production and yield. Even if two-thirds of the seedlings in a reasonable stand are frost-killed, the field usually will produce more when left than if reseeded. The surviving plants will take advantage of the reduced competition for light, moisture and nutrients, and they will grow larger, producing more branches, pods and seeds per pod, thereby compensating for the lost plants. The surviving plants will require five to eight days longer to mature, but a reseeded crop will require an even longer period to reach maturity.

Frost at flowering will delay maturity but results in only minor yield reductions. Frost after flowering, however, can result in significant yield reductions and grade loss. Frost during flowering usually causes flower abortion. Researchers have observed that only plants with open flowers at the time of the frost were affected. Pods lower down on the stems and unopened buds continued to develop normally. Several days after the frost injury, gaps of aborted pods were evident on the stems. The injury was quite evident; all open flowers at the time of the frost showed the damage. The amount of fall frost damage to canola depends on the stage of maturity. A 27 F frost is enough to kill immature seeds containing 50 to 60 percent moisture, while those ready to swath at about 35 percent moisture normally will escape damage. Thus, having uniform stands that ripen uniformly early is important. Uneven stands, with a significant portion of late, immature seeds, may produce seeds of lower quality because the damaged seeds will retain their green color, which will reduce the grade.

 

Story by: Hans Kandel, Extension Agronomist, and Duane R. Berglund, Extension Agronomist Emeritus

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.