Suppression of Anthracnose and Phomopsis Seed Rot on Soybean with Potassium Fertilizer and Benomyl1
- J. W. Sij,
- F. T. Turner and
- N. G. Whitney2
Recent studies linking K with less disease in certain crops have stimulated interest in the beneficial aspects K may play in plant disease protection. The objectives of this 3-yr study were to evaluate the role of K fertilizer on anthracnose [Colletotrichum dematium (Pers. ex Fr.) Grove var. truncatum (Schw.) Arx.] and phomopsis seed rot (Phomopsis sp.) development in field-grown soybean plants [Glycine max (L.) Merr.] and to measure the interaction of foliar-applied benomyl fungicide with soil-applied K fertilizer. The soil, a Typic Agriaquoll, contained low (215 to 278 kg/ha) and high (11 to 96 kg/ha) levels of available K and P, respectively. The experiments included six levels of K, three levels of P fertilizer, and two levels of benomyl fungicide on ‘Davis’ soybean harvested at maturity and 4 weeks later. Anthracnose disease ratings decreased significantly as K rates increased to the maximum of 450 kg/ha. Benomyl and K + benomyl reduced anthracnose substantially more (about 60%) than did K alone. The action of K fertilizer on anthracnose control appeared to be additive to that afforded by benomyl when the soil contained low to medium K. Increasing K fertilizer significantly increased soybean yield by about 700 kg/ha when 220 kg/ha of K fertilizer was applied. Application of benomyl provided an additional yield increase of about 300 kg/ha except at the highest K level. Increasing K up to 330 kg/ha reduced delayed harvest yield losses caused by shattering and weathering. Benomyl and K + benomyl treatments minimized delayed harvest losses, which peaked at a K level of about 220 kg/ha. Phosphorus fertilizer failed to increase yield or prevent shattering. Increasing K reduced Phomopsis sp. in first-harvest seed from 35% to about 1% and in second-harvest seed from about 52 to 28% in plots receiving no K fertilizer and 450 kg/ ha of K, respectively. The addition of benomyl suppressed this pathogen further in first-harvest seed from 12% infected seed to 1% and in second-harvest seed from 40 to 18% in plots receiving no K fertilizer and 450 kg/ha of K, respectively. Phosphorus, however, appeared to slightly enhance Phomopsis sp. development. The effects of residual fertilizer on anthracnose development and yield were evident the following soybean growing season. Although pathogen pressure and environmental conditions play a major role in disease development in soybean, it should be recognized that soil K level can also be an influencing factor.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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