Root Health Management in Raspberry Production Systems
Gigot, Jessica Anne
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Red raspberry (Rubus ideaus) production is a vital component of Washington's agriculture. Two soil borne pathogens, Phytophthora rubi (Pr) and Pratylenchus penetrans (Pp) affect root health in raspberry. In a survey of raspberry production fields, Pr was found at each location. Pp densities were variable, and ranged from 0 to ~7,000/g root tissue across survey locations. Phytophthora spp. has a negative correlation with percent silt (P=0.0041), while Pp had a negative correlation with percent clay (P=0.0012) and a positive correlation with percent organic matter (P=0.006). In controlled studies it was found that Pr at densities > 10 oospore/gram of soil was very pathogenic to raspberry `Meeker' roots. Pp population densities also had a linear relationship with root rot symptoms, but no interaction between these pathogens was detected. Several chemical fumigant alternatives to methyl bromide exist for control of raspberry nursery pests in northwestern Washington. Telone C-35 (65% 1,3-dichloropropene:35% chloropicrin), and Midas 50:50 (50%iodomethane: 50% chloropicrin) applied at 39 gal/a and, 250 lb/a respectively, in combination with both (virtually impermeable film) VIF and (high density polyethylene) HDPE films were effective against Pr and Pp without negative effects on marketable canes. To increase the sensitivity of Pr inoculum assessment, a quantitative real-time assay was developed. Real-time PCR results were similar to bioassay results for all treatments tested. Nursery growers are considering alternatives, however the majority of growers still would prefer methyl bromide and do not believe in the environmental human health issues at the root of its phase-out. Brassicaceous seed meals are an alternative to synthetic chemical fumigation. Two species (B. juncea and S. alba) effectively controlled Pr and Pp at rates of 0.5 and 1.0% v:v, respectively, in greenhouse experiments. Control of Pr with these seed meals was enhanced with solarization to a depth of 15 cm, only. Nematode community abundance and compostion were affected differently by the seed meals. Brassica juncea eliminated all nematodes 1 wk after application and increased the overall enrichment index (EI) at 5 wk. Sinapis alba also reduced nematode population densities at 1 wk, and increased the structure index (SI) at 5 wk. Phytotoxicity (> 40% plant damage) to raspberry `Meeker' was observed 1 wk after the application of S. alba (1% v:v) only and phytotoxicity did not extend beyond one week.