July 28, 2008

Patrick Beauzay                                                     Janet Knodel

Extension Entomology Research Specialist     Extension Entomologist

701-231-7064                                                         janet.knodel@ndsu.edu

patrick.beauzay@ndsu.edu

The only time yield loss is noticeable is when larvae burrow into unopen buds, preventing proper head development. The larvae normally do not feed on developing seeds but confine feeding activities to the fleshy part of the head. The larva has a dark head capsule with a smooth, cream-colored body and is 0.31 to 0.43 inch (8 to 11 mm) at maturity (see photograph).

There are two generations of sunflower bud moth in North Dakota. Adults emerge from overwintering pupae between the last week of May to mid-June. A few days after adult emergence, eggs are deposited on the terminals of immature sunflower or on the receptacle of mature sunflower. Eggs also are deposited in leaf axils. The hatched larvae begin tunneling into the sunflower plant. The initial infestation in mid-June is characterized by an entrance hole surrounded by black frass, or insect excrement. Mature larvae pupate within the sunflower plant. Pupae move to the opening of the entrance holes formed in the stem or head tissue so that adults can emerge easily. The second generation adults appear in August. Infestation by the second generation larvae is not economically important.

A field monitoring scheme and economic threshold has not been established for this insect since it is not of economic significance most years. Insecticide use is NOT recommended for control of sunflower bud moth, because the larvae are protected when feeding within the sunflower plants. As a result, insecticides will have limited efficacy.

Joel Ransom

Extension Agronomist - Cereal Crops

More than half of the state is now rated abnormally dry or drier by the US Drought Monitor (http://www.drought.unl.edu/dm/DM_highplains.htm) and nearly a third of the state is under severe drought. Corn is one of the most water efficient crops grown in North Dakota. Nevertheless, it has a high water requirement because of its high yield potential and can be significantly impacted by drought. The impact of drought on corn growth and yield varies considerably depending on its timing and severity. Research has shown that there is little impact of drought on corn growth during early vegetative stages. During late vegetative development, however, short periods of drought stress (four days of sufficient stress to cause leaves to curl) during this growth stage can reduce yields by 5-10%. Currently most of the corn in North Dakota is in the 8 to 12 leaf stage. Kernels per cob are being set during this stage until just before silking, so drought stress now can impact the size of the cob. Drought stress during tassel emergence has the potential to reduce yields by 10 to 25%. The most sensitive period for drought stress in corn is during the period between silk emergence and the blister stage where yield losses between 40-50% can occur. Corn is most sensitive to drought during this stage because the male and female flowers are separated by a considerable distance and pollen and silks are sensitive to hot and dry conditions. When corn is severely stressed prior to flowering, silk growth is delayed and pollen shed will occur before the silks have emerged, resulting in barrenness. Silks can also dry before they are pollinated resulting in poor fertilization and missing kernels. Abortion of developing kernels is common, particularly towards the tip of the ears, with drought stress during early grain fill. Since the corn plant has the capacity to store considerable reserves in the stem, yield losses when drought stress is delayed until the dough stage usually are in the 20-30% range. These yield losses discussed above can be additive if stress occurs at more than one growth stage. With about half the growing season still ahead of us, the potential for yield losses due to drought appear to be quite high for a large part of the state unless we get some timely rains.

During the first stage of stress, the upper leaves curl or roll towards the midrib during the hottest part of the day (see attached photo). If stress continues, premature leaf death begins at the bottom of the plant and proceeds upward. Leaf death is the first sign of permanent damage to the plant. With severe stress, the upper leaves roll so tightly that they appear like "onion leaves". With less leaf area capable of photosynthesis, grain filling is slowed even while maturing at an accelerated pace.

Carbohydrates that had been stored in the stem earlier in the season are moved to the developing ear. Not surprisingly, drought stressed crops are more prone to lodging because of poor stalk health. There may be some kernel abortion in the tips of the ears, but for the most part, kernel numbers are not reduced significantly with late season drought. Yield losses will largely be due to reduced kernel size and reduction in test weight. The amount of reduction will be related to the amount of stress prior to harvest.

Ventenada control data is also limited. One research report from University of Idaho in 2002 shows: