Biodegradable mulch performed comparably to polyethylene in high tunnel tomato (Solanum lycopersicum L.) production.

BACKGROUND: High tunnels in the cool climate of north western Washington state improve the growing environment for crops otherwise suited to warmer climates. Biodegradable mulch may improve the sustainability of high tunnel vegetable production if it performs comparably to polyethylene. Four biodegradable mulch treatments (BioAgri, BioTelo, WeedGuardPlus and SB-PLA-10/11/12) were compared to black polyethylene and bare ground in high tunnels and open field settings to assess the impact of production system and mulch treatment on weed control, tomato yield, and fruit quality. RESULTS: Fewer weeds grew in high tunnels than in the open field. High tunnels increased total and marketable fruit yields and increased individual fruit weight. High tunnel production increased juice content and pH of tomato fruit, but decreased total soluble solids, titratable acidity, and total phenolics compared to the open field. All mulch treatments except SB-PLA-10 controlled weeds. BioAgri, BioTelo and polyethylene increased total yields by 20%, though marketability was reduced 14% compared to bare ground and WeedGuardPlus treatments. CONCLUSION: High tunnels can improve tomato yield and affect fruit quality in north western Washington. Biodegradable plastic mulches performed comparably to polyethylene in weed control, tomato yield, and fruit quality and may, therefore, improve the sustainability of high tunnel vegetable production.

Control of Potato Tuber Rots Caused by Oomycetes with Foliar Applications of Phosphorous Acid.

Phosphorous acid for control of tuber rots caused by Phytophthora infestans, P. erythroseptica, and Pythium ultimum was applied to foliage of potato cultivars at various application timings and rates under growing conditions in the Pacific Northwest at Othello and Mount Vernon, WA, and Bonners Ferry and Aberdeen, ID in 2001 to 2003. Efficacy was assessed by artificially inoculating harvested tubers. Mean incidence and severity of late blight tuber rot in tubers inoculated with US-8 and US-11 isolates of Phytophthora infestans usually were significantly less when the foliage from which the tubers were obtained was treated with phosphorous acid than when it was not treated at all locations. With two applications of phosphorous acid, late blight tuber rot in the tuber-resistant cv. Umatilla Russet was significantly less than for Ranger Russet. For phosphorous acid at a rate of 9.37 kg a.i./ha, late blight tuber rot control achieved with two applications at 2-week intervals was not consistently improved across locations by making an additional application 2 weeks later. In 2003, incidence and severity of late blight tuber rot did not differ significantly between the rates of 7.49 and 9.37 kg a.i./ha at both Othello and Mount Vernon. Late blight tuber rot incidence and severity were significantly less at a rate of 7.49 kg a.i./ha when the application schedule began at initial tuber bulking rather than when the first application was made 4 weeks after initial tuber bulking at Othello, but not Mount Vernon. Incidence of pink rot was significantly less in inoculated tubers from plots treated with three applications of phosphorous acid than in tubers from nontreated control plots at Mount Vernon in 2002 and 2003, Bonners Ferry in 2002, and Aberdeen in 2003. Pink rot severity was reduced significantly by both two and three phosphorous acid applications at Mount Vernon in 2002. Pink rot incidence, but not severity, was reduced significantly at all timings when either 7.49 or 9.37 kg a.i./ha was applied at Mount Vernon in 2003. Control of Pythium spp. by phosphorous acid was not evident in this study. Total tuber yield at harvest did not differ significantly among the phosphorous acid treatments and the nontreated control at Othello and Mount Vernon in 2001 and 2002.

Foliar Fungicides as Protective Seed Piece Treatments for Management of Late Blight of Potatoes.

Fungicides receiving Section 18 emergency exemptions for management of the foliar phase of late blight of potato were evaluated as protective treatments for control of tuberborne inoculum of Phytophthora infestans in greenhouse and field studies. Three Section 18 products, Acrobat MZ (dimethomorph + mancozeb), Curzate M-8 (cymoxanil + mancozeb), and Tattoo C (propamocarb hydrochloride + chlorothalonil), when applied to the seed piece prior to inoculation with P. infestans, significantly (P ≤ 0.05) increased sprout emergence, compared with the inoculated water control. Of the three Section 18 products, Curzate M-8 was frequently the most effective. The increase in plant emergence with the protective seed piece treatment was seen with cultivars that differ in susceptibility to late blight, two genotypes (US-8 and US-11) of P. infestans, zoospore and sporangial inocula, and at different inoculation sites on the seed piece. In greenhouse studies, percent emergence with the protective seed piece treatments averaged 74% for cv. White Rose and 44% for cv. Shepody, compared with 9 and 8% for the inoculated water control of the respective cultivars. In field studies, when inoculum was placed either adjacent to or 4 cm away from the sprout, plant emergence of the inoculated water control was 12 and 36%, respectively. Application of the fungicides to the seed piece prior to inoculation increased emergence by an average of 700 and 212% for the respective inoculation sites. There was no evidence for translocation of the fungicides to the emerging foliage in concentrations high enough to prevent foliar infection from airborne inoculum of P. infestans. Control of tuberborne inoculum of P. infestans with appropriate seed piece treatments will result in an increase in plant emergence and improved crop uniformity.