GEORGIA / FLORIDA
UNIVERSITY OF GEORGIA
Department of Agronomy, Griffin, GA 30212, USA.
J.W. Johnson, R.D. Barnett, B.M. Cunfer, and G.D. Buntin.
The 2002 Georgia winter wheat crop was grown on about 350,000 planted acres, an increase of 15 % over 2001. Oat acreage was 85,000 acres, 15 % less than in 2001. Acres planted to rye were 250,000, 17 % less than last year. The crop production for wheat resulted in a state average yield of 41 bu/acre. The autumn planting conditions were hot dry soils. Most of the planting was delayed by at least 2 weeks past optimum. Overall, the season was characterized by mild and dry winter conditions followed by a dry and hot spring. Lack of vernalization was a problem especially for late-maturing cultivars. A spring freeze occurred on 22-23 March with temperatures around 26 F. Dry conditions prevailed through the grain-filling stage and hastened harvest. Yield and test weight were reduced significantly due to the freeze damage.
Horizon 474 (FLX474-1) oat was released as an exclusive cultivar. A winter oat with excellent test weight, Horizon 474 has good crown rust resistance and early maturity. Horizon 474 was selected from the cross 'Coker85-18//Coker 78-28/Coker 79-26'. The cultivar is most similar to Florida 501 but has white seed.
Double cropping is an important practice in areas of the southern U.S. where length of growing season and adequate rainfall or irrigation permit timely stand emergence and development and maturity of a summer crop. The predominant double-crop sequence is winter wheat and soybean, although grain sorghum and cotton are sometimes grown as a double-crop with wheat. The advantages of double cropping are increased cash flow for producers, reduced soil erosion and water loss because of ground cover most of the year, and cost savings from a more intensive use of the land and better utilization of crop inputs, labor, and capital investments. However, double cropping essentially can result in continuous production of crops in the same field each year, which can cause a build up of damaging levels of pathogen, insect, and weed populations. Indeed, in the 1970s and 1980s, continuous double-crop production of winter wheat resulted in serious damage in many fields by take-all root and crown rot and by devastating outbreaks of the Hessian fly. Incorporating alternative crops that are culturally and biologically compatible with a soybean/wheat double-crop system could help reduce pest incidence and severity and also provide farmers with commodity marketing alternatives. Canola (Brassica napus L.) as an alternative, winter-grain crop and pearl millet (Pennisetum glaucum (L.) R. Br.) as a new, alternative summer crop may effective break pest cycles in double-cropped soybean and winter wheat.
We established a 5-year study in the Coastal Plain region of GA to examine the effects of incorporating canola and pearl millet in multiple-year rotational sequences on the agronomic performance and pest incidence and severity in a wheat-soybean double-crop system. The experiment was conducted on a Greenville sandy loam at the Southwest Branch Experiment Station near Plains, GA. Twelve crop sequence and rotational treatments were established in an RCB design with four replications. Rotations included winter wheat, winter canola, winter rye, or fallow and summer crops were soybean or pearl millet for grain production.
Winter wheat productivity was affected by the previous crop sequence and rotation history. A single year of canola production greatly reduced the severity of infection take-all root and crown rot in wheat. Wheat rotation with canola every few years was very effective in suppressing take-all stem and root rot. Canola as the previous winter crop reduced winter infestations and, to some extent, spring infestations of Hessian fly. Furthermore, the wheat-soybean rotation had lower winter infestation levels of the Hessian fly than a wheat-millet rotation. Reduced Hessian fly infestation in rotations with canola is understandable because of the lack of a host plant. The reason for increased infestation levels following millet compared with soybean is not clear. Possibly, the herbicide regime in millet did not control volunteer wheat in late summer and in soybean, thereby providing a bridging host for the first autumn generation of Hessian fly, which develops in volunteer wheat before planting of the winter wheat crop.
Canola grain yields were not affected by the previous summer and winter crop or the cropping sequence in any year. Pearl millet stands were lower following canola than wheat in 2 of 4 years. Stand loss was mainly the result of seedling feeding damage caused by false chinch bugs, (Nysius raphanus Howard) following canola. Soybean stands also were reduced consistently by 1825 % following canola as compared with small grains in all years except 1998. Except for seedling damage by false chinch bugs, the sequence of the previous winter crop had little consistent effect on insect populations on soybean or grain millet or on soybean diseases.
These results show that continuous planting of a crop can enhance host-specific pests such as Hessian fly and take-all disease in wheat. Stands of soybean and grain millet usually were reduced when planted into canola stubble as compared to winter wheat, rye, or fallow. However, the previous cropping sequence did not reduce grain yields of pearl millet or soybean. Therefore, rotating canola with wheat to disrupt pest cycles in wheat can be done without detrimental, limiting effects on subsequent soybean or millet crops as long as plant populations are not near or below the minimum for a full stand.