In summer 1991 malformations of the ears and the last internode, the peduncle, which carries the ear, of winter wheat were observed. Possible causes about the role of special herbicides in connection with extreme temperatures (frost below 7 degrees) are discussed. Such abnormalities caused by herbicides can be confused with symptoms of Sclerophthora macrospora (crazy-top), but attempts to associate this pathogen with the described deformities failed

Experiments were conducted to determine the influence of nitrogen (N) fertility and winter wheat cultivars on weed infestations in a winter wheat-ecofallow sorghum-fallow rotation near North Platte, NE. Centurk 78 and Lancota winter wheat suppressed density and growth of barnyardgrass and green foxtail significantly more than Eagle winter wheat before and after wheat harvest. Increasing N rates applied to winter wheat decreased annual grass weed population and weed yields. However, 67 and 101 kg N ha-1 reduced winter wheat grain yields compared to 34 kg N ha-1. Plots treated at 2.8 plus 0.3 kg ai ha-1 of atrazine plus paraquat 31 d after wheat harvest had more barnyardgrass before grain sorghum planting in 1983 than plots treated 17 d after wheat harvest but the reverse was true for green foxtail after grain sorghum emergence in 1984. Increasing N rates from 34 kg ha-1 to 67 and 101 kg ha-1 in the previous wheat crop decreased weed density before and after grain sorghum planting. There was no advantage in weed control in the grain sorghum from applying N to winter wheat in the fall vs. spring.

In the paper results of an experimental study of the change in winter wheat and winter barley frost resistance as related to damping off conditions are presented. As influenced by the length of damping off conditions effect on the plants, their resistance was found to distinctly reduce. Thus critical temperature of winter killing in winterhardy winter wheat and winter barley varieties was observed after 60 days of the crops remaining under damping off conditions to reduce - by 6-7 degrees C, in mediom winterhardy varieties - by 6-9 degrees C, whereas in winter wheat and winter barley varieties with narrow base of winter hardiness - by 7-12 degrees C.

In the paper results of an experimental study of the change in winter wheat and winter barley frost resistance as related to damping off conditions are presented. As influenced by the length of damping off conditions effect on the plants, their resistance was found to distinctly reduce. Thus critical temperature of winter killing in winterhardy winter wheat and winter barley varieties was observed after 60 days of the crops remaining under damping off conditions to reduce - by 6-7 degrees C, in mediom winterhardy varieties - by 6-9 degrees C, whereas in winter wheat and winter barley varieties with narrow base of winter hardiness - by 7-12 degrees C.

Data on experimental material as to the effect of ice crust, differing in thickness and length, on resistance to winter wheat overwintering are adduced. Ice crust 1 cm thick was found to have no essential effect on winter wheat plants under any duration of its effect. Ice crust 5 cm thick results in killing 20-40% of winter wheat plants even when its effect is 30 days. Most negative effect on productivity components has ice crust 30 cm thick for the period 60 days and the crust 5 cm thick even after the period 30 day long.

The influence of several four leveled crop rotations including different rates of cereals on the coverage level through weeds, the population dynamic and cereal aphids, and their predators as well as the crop yield was studied in winter wheat in 1989 and 1990. The coverage level through weeds was a little higher in a crop rotation with organic fertilization and a low cereal portion (crop rotation C: sugar beets - winter wheat - maize -maize) than in a crop rotation with a larger portion of creal crops (crop rotation A: sugar beets - oats - winter wheat -winter barley). The cereal aphids Sitobion avenae (F.), Metopolophium dirhodum (Wlk.) and Rhopalosiphum padi (L.) occurred in both years and S. avenae was the most encountered of all species. The obtained results indicated that the crop rotation affected the population dynamic of the cereal aphids in winter wheat. The highest number of aphids was observed in winter wheat of crop rotation A in 1990. On the other hand, the lowest number of aphids was found in crop rotation C, being more infested with weeds. It could be shown, that the most abundant predators in all crop rotations were Coccinellidae, especially Coccinella septempunctata (L.), followed by Syrphidae and Chrysopidae. The number of predators which were collected with sweep nets during June and July were lower in 1989 than in 1990. Significantly more predators were observed in winter wheat of crop rotation C (17 individuals) than in winter wheat of rotation A (9.5 individuals) in 1990. In both years the wheat yield in crop rotation C (65.3 dt/ha and 72.6 dt/ha) was higher than in rotation A (56.8 dt/ha and 66.4 dt/ha)

The investigations were done in 1987-89. It was found, that depending of plow of 25 to 35 cm influence on decrease yielding of winter wheat, oats and field pea. Shallow plow (15 cm) in relation to deep plow (25 cm) influenced on decreased yields of winter wheat and field pea. Use plow with subsoiler caused decreased yielding of winter wheat more then oats yielding but increased yields of field pea. Tillage by rotary cultivator instead by plow in maximum influenced on decrease yields of cultivated crops

The density of cultivation, the high level of yield and the necessary nitrogen fertilizer are responsible for the intensive attack of winter wheat by insects in the south of Lower Saxony. Considering the corresponding economic threshold, aphids have to be controlled nearly every year. These thresholds can't be used if yellow dwarf virus could be transmitted in the follow of mild winters or if strong and continuous by Metopolophium dirhodum is found beneath the leaves. In 1989 and 1990 we had a strong attack of yellow dwarf in early sown winter wheat infested in autumn and in early spring, but additional to this all winter wheat was infested in May and at the beginning of June. The loss of yield was considerable, also because of the late infestation. Haplodiplosis equestris can be observed every year too. This insect appears especially in rotation with frequent wheat cultivation. The three fields rotation of sugar beet or rape, winter wheat and winter barley seems to be less endangered than a rotation with wheat dominating. On dark and similar soils Phorbia coarctata causes damage in late sown winter wheat. Resolidifying of the seed bed seems to be a suitable preventive measure. In very endangered fields the additional insecticide treatment of the seed reduces the damage

In 1981-83 under the different agroecological conditions on representative soil types: alluvial soils (NP), alluvial gley soils (NPg) and illimerized soils (IP) in the East Slovak Lowlands, problems of crop rotation were examined. The dependence between the yield of winter wheat and the infestation by stem break was observed. With the higher intensity of plant infestation the yield of winter wheat decreased by 19.3 percent (1,2 t.ha-1) to 46.8 percent (3,4 t.ha-1) depending on the soil types. The greatest yield depression of winter wheat was found out in low fertility soils

Data on experimental material as to the effect of ice crust, differing in thickness and length, on resistance to winter wheat overwintering are adduced. Ice crust 1 cm thick was found to have no essential effect on winter wheat plants under any duration of its effect. Ice crust 5 cm thick results in killing 20-40% of winter wheat plants even when its effect is 30 days. Most negative effect on productivity components has ice crust 30 cm thick for the period 60 days and the crust 5 cm thick even after the period 30 day long.