Influence of Soil Temperature and pH on Pratylenchus Penetrans and P. crenatus in Alfalfa and Timothy.

Numbers of Pratylenchus penetrans in alfalfa and timothy, and to a lesser extent P. crenatus in timothy, increased substantially as temperature increased from about l0 C to 30 C. However, P. crenatus in alfalfa decreased in number as temperature increased. Mobility of P. crenatus in vertical soil columns decreased as temperature increased from 9.5 C to 28.5 C. Raising the soil pH from 5.0 to 6.9 in which alfalfa was grown increased the numbers of P. penetrans and greatly reduced the numbers of P. crenatus. The numbers of both nematode species in timothy were reduced significantly as soil pH was increased. The optimum soil pH for movement of P. penetrans was 6.0. Pratylenchus crenatus moved equally well over a range of pH 5.0 to 7.0.

Effects of Phenamiphos, Methyl Bromide, and Fallowing on Pratylenchus Penetrans, Yield of Medicago sativa, and Fusarium Infections.

A field study was made of the effects of a residual nematicide (phenamiphos), a fumigant (methyl bromide), and fallowing on the number of root lesion nematodes (Pratylenchus penetrans), forage yields of alfalfa, and the occurrence of Fusarium spp. in plant roots and soil. Fallowing controlled nematodes initially, but by the end of the second growing season, nematode numbers were as high as in plots which had grown a nematode-susceptible crop. Forage yield was greater in fallowed plots only for the first cut in the year after seeding. Fusarium in alfalfa roots and soil was not reduced by fallowing. Phenamiphos reduced nematode numbers, increased forage yields in 2 of 4 years, and reduced Fusarium infections of taproots. Soil fumigation with methyl bromide gave the best control of nematodes and Fusarium and gave significantly higher forage yields for the 4 years of study following fumigation. The 34% increase in alfalfa yield from fumigated plots over the 4 years indicates that the yield of alfalfa is being reduced significantly by microorganisms. The study does not establish the relative contributions of the root lesion nematodes and Fusarium spp. to the reduction.

Effects of potassium fertilization and Pratylenchus penetrans on yield and potassium content of red clover and alfalfa.

Red clover and alfalfa were inoculated with Pratylenchus penetrans and grown in an Alberry sandy loam soil to which potassium (K) was added at seeding at 0, 41.5, 83, and 166 microg/g. In one experiment with alfalfa, additional K was added after each forage cut to replace that which was removed. Nematode populations were not consistently affected by K fertilization. Nematode infection stunted red clover and alfalfa and resulted in lower yields at all K levels, except for alfalfa at the lowest K level. Nematode infection had no effect on taproot yields. However, it resulted in lower rootlet yields from red clover at all K levels, lower rootlet yields from alfalfa only at the highest K level in one experiment, and lower rootlet yields at all but the lowest K level in a second experiment, potassium fertilization enhanced yield of red clover and alfalfa. Yield increases were smaller from increased K fertilization in nematode-infested soil than in noninfested soil. Pralylenchus penetrans had little effect on the K content of red clover or alfalfa. The stunting of plants from nematode infection resulted in less K being removed from the soil.

Efficacy of multiple applications of oxamyl and phenamiphos for control of Pratylenchus penetrans in birdsfoot trefoil.

Preplant soil applications of granular phenamiphos effectively reduced Pratytenchus penetrans in soil during the seeding year and 1 year after, and in the roots of birdsfoot trefoil 2 years after seeding. Forage yields were increased in the season following application of phenamiphos, but stands of plants/m(2) were not greater (P = 0.05) than those in the checks 1 and 2 years after treatment. Additional spring applications of phenamiphos 1 and 2 years after seeding further reduced numbers of nematodes in the soil but did not improve forage yields or plant stand over that of a single application. Broadcast preplant soil sprays of oxamyl followed by several foliar sprays at different rates and frequencies of application over a 3-year period restricted populations of P. penetrans in the soil and roots of birdsfoot trefoil but did not consistently result in increased forage yields. Stands of birdsfoot trefoil continued to decline each year even with oxamyl treatments.

Effects of Soil pH on Reproduction of Pratylenchus penetrans and Forage Yield of Alfalfa.

'Vernal' alfalfa was grown for 30 weeks in nematode-free soil and in soil infested with Pratylenchus penetrans. Charlottetown fine sandy loam soil was used at its pH of 4.4 and at adjusted reactions of 5.2, 6.4 and 7.3. Nematode reproduction was significantly greater at pit 5.2 and 6.4 and was not related to alfalfa root production over the full pH range studied. A significant nematode infestation X soil pit interaction on forage yield was recorded. Nematode infestation significantly decreased forage yields at ptt 5.2 and 6.4 but not at pH 4.4 and 7.3.