ISSUE 13 July 27, 2000
SMALL GRAIN DISEASES
Root Rot, Bacterial Blight: As wheat and barley crops are entering dough stages, diseases are very evident in many small grain fields. White heads on bleached plants are very common, due to root rot infections (see Crop and Pest Report #11, July 13, 2000). Water saturated soils followed by high temperatures and heat stress contributed to the root rot levels we are seeing this year. Bacterial leaf blight also is severe in some areas. Bacterial infections that occurred during recent storms may be evident on leaves of some varieties, such as Russ spring wheat. The whole leaf or part of the leaf exhibits brown, shiny streaking along the leaf veins. Neither root rot or bacterial blight will be controlled with foliar fungicides. If growers used foliar fungicides and have root rot or bacterial blight, they may think their fungicides did not do the job expected. Preliminary evaluations of fungicide plots at NDSU indicate otherwise, however. Fungicides are reducing scab and controlling leaf rust and Septoria.Small Grain Survey Results: The following reports were submitted by NDSU Extension Scouts this past week (ending July 21st). Southwest and West Central Districts:
North Central and Northwest Districts:
Laura Neal, Holly Semler, and Allison Marsland surveyed fields in McHenry, Pierce, Renville, Bottineau, Rollette, Williams, and Divide counties this past week. Diseases observed included wheat leaf rust (range of severity on the flag leaf from 0-19%), Septoria, tan spot, head scab, root rot, wheat streak mosaic, barley yellow dwarf, bacterial blight, bacterial black chaff, and loose smut. Field severity of scab ranged from 2-6%and was observed in 20% of the fields surveyed.
Loose smut levels ranged from 4-30% of tillers smutted in those fields with symptoms. The field scouts also found wheat stem maggot symptoms in 45% of the fields, with up to 18% of stems in one field showing the typical white heads and chewed stem at the first node.
Extension Plant Pathologist
PASMO DISEASE ON FLAX
Pasmo disease has been showing up at several of the research
extension centers and at least one phone call apparently was about pasmo. Pasmo, caused by
Septoria linicola, is spread by splashing water, and so is most likely to develop
in areas that have had frequent rain showers. It is also more likely to develop in flax
that has lodged. First symptoms are circular brown spots on the leaves. The older leaf
spots will develop tiny black fruiting bodies the size of finely ground pepper. The
bodies may be arranged in a target pattern. As the crop matures, infections develop on the stem. These infections result in a botchy pattern of brown and green on the stem. Fruiting bodies may form on the stem. Severely infected plants may turn completely brown. Bolls may be infected, and the pedicels that bear the bolls may be infected, resulting in bolls dropping during wind or rain.
Biology. The fungus survives on flax stubble, and can spread from the stubble to a new crops, especially if flax is on a short rotation in a field. The fungus may also be seedborne, as well as be borne on small bits of crop debris mixed with the seed. Spread is primarily by splashing water, and disease development is favored by frequent rainstorms.
Disease Management. Bury diseased flax stubble after harvest and avoid planting flax on the same land for several years. Plant flax early. Plant well-cleaned seed that is free of shriveled seeds and small bits of crop refuse. Avoid using seed from a diseased field as seed. Use a seed treatment fungicide. Harvest diseased fields as soon as practical, as delayed harvest may result in severe loss of bolls in heavy windstorms.
Aster yellows is beginning to show up in canola and flax. For the most part, infection levels appear to be low. It is likely to show up in other crops as well, and also some ornamentals. The aster yellows phytoplasma is transmitted by the aster leafhopper as well as several other species of leafhopper. Although the aster leafhopper may survive the winter in the egg stage in our area, most aster yellows phytoplasma is believed to be borne by leafhoppers migrating in from farther south (see entomology section of Crop and Pest Report No. 4 for details).
The aster yellows phytoplasma has an extensive host range, including various broad leaved crops and cereals. It causes shortened internodes which may result in "witches brooms", purplish coloration of the upper portions of plants, and yellow growth terminals. It frequently causes flowers to be greenish-yellow or to have greenish-yellow sectors in them.
Canola. Upper portions of flowering shoots develop hollow, blue-green bladder-like structures in place of pods. Upper flowers may be greenish and upper internodes may be stunted, resulting in a bushy appearance. The disease was common in 1999 and appears to be fairly common again in 2000.
Flax. Shoots and flowers are yellow or greenish yellow. Seed set may not occur in diseased portions of plants.
Potato. Called purple top because the upper foliage develops a reddish or purplish color. The upper leaves also may roll upward. Small tubers (serial tubers) may form in the axils of the leaves.
Sunflower. Pie-shaped sections of the head may be green or the entire head may be green. Leaf-like structures may develop in the affected areas.
Extension Plant Pathologist
PLANT DIAGNOSTIC LAB REPORT
The diagnostic lab has become a jungle again, the plants are tall and coming in by the dozen or so each day now. These are some of the samples that have come through the lab this past week: Soybean - growth regulator herbicide injury, iron chlorosis/wet soils, root rot (Rhizoctonia and Pythium, Phytophthora); Potato - late blight, blackleg, Rhizoctonia/wet soils; Dry beans - growth regulator herbicide injury, bacterial brown spot; Corn - growth regulator herbicide (probable dicamba), wind injury; Wheat - BYDV, common root rot, septoria leaf spot, fusarium head blight; Sunflower - growth regulator herbicide, possible Assert injury; Sugarbeet - root rots (Aphanomyces, Rhizoctonia, and Pythium); Maple - iron chlorosis; Oak - oak anthracnose; Elm - dutch elm disease; Raspberry - anthracnose; lawn - patch disease complex, salts injury.