Nonchemical, Cultural Management Strategies to Suppress Phytophthora Root Rot in Northern Highbush Blueberry

Phytophthora cinnamomi Rands causes root rot of northern highbush blueberry (Vaccinium corymbosum L.), which decreases plant growth, yield, and profitability for growers. Fungicides are available to suppress the disease, but are prone to development of resistance in target pathogens and cannot be used in certified organic production systems. Alternative, nonchemical, cultural management strategies were evaluated to reduce phytophthora root rot in a field infested with P. cinnamomi. The field was planted with ‘Draper’ blueberry, which is highly susceptible to the pathogen. The soil was either amended with gypsum or not before planting, and the plants were irrigated using narrow (adjacent to plant crown) or widely spaced (20 cm on either side of the plant crown) drip lines and mulched with douglas fir sawdust or black, woven geotextile fabric (weed mat). A fungicide control treatment was also included in the study and consisted of applying two conventional fungicides, mefenoxam and fosetyl-Al, to plants irrigated with narrow drip lines and mulched with sawdust. Initially, root infection by P. cinnamomi was lower with the combination of gypsum, wide drip lines, and sawdust mulch than with any other treatment, except the fungicide control. The soil under weed mat accumulated more heat units than under sawdust and resulted in faster hyphal growth by the pathogen. However, plant growth was similar in both mulch types. The effects of drip line placement and gypsum, on the other hand, were interactive, and plants grown with a combination of wide drip lines and gypsum produced the greatest amount of biomass among the cultural treatments. Narrow drip lines negated the disease-suppressive effects of gypsum by moving zoospore-inhibiting Ca2+ away from the plant root zone, and also resulted in wetter soil near the crown of the plants, which likely promoted zoospore discharge and root infection. However, wide drip lines resulted in N deficiency symptoms during the first year after planting and, therefore, resulted in less plant growth than the fungicide control. Thus, if N is managed properly, this study suggests that concerted use of gypsum and wide drip lines can help suppress phytophthora root rot in northern highbush blueberry and increase production in field soils where the pathogen is present.

Gas exchange parameters in leaves and ears of winter wheat Tricitum aestivum L. and its productivity under fungicide control conditions

A research experiment was conducted in which rates of photosynthesis and transpiration were measured in leaves and ears of two winter wheat varieties grown under fungicide control conditions and without fungicide control. A LI-COR 6400 portable gas exchange system was used in the investigations. In most cases the fungicide Juwel was shown to have no effect on the gas exchange processes, whereas the other of the fungicidal agents applied - Swing - significantly decreased the gas exchange rates measured. Measurements of gas exchange parameters in ears showed that the intensity of gas exchange was low, in particular at the later stage of ear development. But the applied fungicide caused higher release of CO₂ into the atmosphere than its uptake. Furthermore, the applied fungicides were found to significantly increase grain yield compared to the control treatment, both in the first and second year of the study. Among the tested varieties, 'Nutka' was characterized by higher productivity, in spite of lower 1000 kernel weight. However, this cultivar developed longer ears with a larger amount of grains.

Assessing the Adequacy of the Simulation Model LATEBLIGHT Under Nicaraguan Conditions

In this study, the adequacy of the late blight simulation model LATEBLIGHT (version LB2004) was evaluated under Nicaraguan conditions. During 2007 to 2008, five field experiments were conducted in three potato-production regions in northern Nicaragua. Two susceptible (‘Cal White’ and ‘Granola’) and one resistant (‘Jacqueline Lee’) potato cultivars were evaluated without use of fungicides and with three application intervals (4, 7, and 14 days) of the fungicide chlorothalonil. The simulation model was considered adequate because it accurately predicted high disease severity in susceptible cultivars without fungicide protection, and demonstrated a decrease in the disease progress curves with additional fungicide applications, similar to that observed in the plots. The model also generally predicted inadequate fungicide control, even with a 4-day spray interval, which also occurred in the field. Lack of adequate fungicide protection would indicate the need for cultivars with higher levels of durable resistance, and that farmers should consider more effective fungicides applications (higher dosages or different chemistries) if susceptible cultivars are used.

Cover Crop Mulch and Fungicide Program Affect Development of Septoria Leaf Spot and Marketable Yield in Processing Tomato Production

The development of septoria leaf spot in processing tomatoes grown on conventional (bare soil) beds or beds with chemically or mechanically killed winter rye (Secale cereale L.) and hairy vetch (Vicia villosa Roth) cover crop mulch with or without fungicide was examined. The two fungicide treatment programs included fungicide applied weekly (7 d) and a no fungicide control. In mulch bed systems without fungicide, septoria leaf spot caused ≈50% defoliation 10 and 28 d later in 1997 and 1998 than in the conventional system, respectively. In both years, area under disease progress curve (AUDPC) values for septoria leaf spot development were lower with the presence of a chemically or mechanically killed mulch compared with the conventional bed system when no fungicide was applied. In 1997, there were no significant differences in AUDPC values for septoria leaf spot development when fungicide was applied weekly. In 1998, AUDPC values were lower in both mulch systems compared with the conventional bed system when fungicide was applied weekly. At harvest in both years, defoliation was highest in the no fungicide control treatment. In 1997, marketable yield was significantly higher in both mulch systems compared with the conventional bed system. Conversely, in 1998, marketable yield was significantly higher in the conventional bed system than in either mulch bed system.