Prevention of phytotoxic effect of fungicides applied via drenching for powdery mildew control on pepperPlant Protection, Vegetables
תחום או ענף הגה"צ; ירקות
תאריך עדכון 14/3/2012
Prevention of phytotoxic effect of fungicides applied via drenching for powdery mildew control on pepper
Shimon Pivonia, Rachel Levite, Ami Maduel – Central and Northern Arava R&D
E-mail address for correspondence: ShimonP@arava.co.il
Powdery mildew is the main canopy disease of pepper crops in the Arava. This disease is caused by the fungus Leveillula taurica, which develops inside the leaf tissue and destroys that tissue. The mycelia and spores that emerge from the leaf provide the characteristic white dusting that looks similar to flour. (Translator’s note: The Hebrew term for “powdery mildew” is derived from the word for “flour”.) The disease appears every growing season. Pepper is planted in the Arava beginning in late July and powdery mildew appears in the fields when the temperature drops. There is a 6 to 8 week period during which conditions for powdery mildew development are generally optimal. After this period, the rate of powdery mildew development decreases.
In experiments carried out at the R&D Authority, it was found that the disease could be prevented and/or its severity could be significantly reduced throughout the season if disease development could be inhibited during this critical period. Similarly, it was found that a single drench application of fungicide could protect pepper plants against powdery mildew for 3 to 4 weeks. Two properly timed fungicide drenches can protect the plant from powdery mildew throughout the period of optimal disease development. The use of this method eliminates the need for many sprays and improves control efficacy. As the use of this technique has spread to the majority of pepper plots in the Arava, we have observed some incidents of phytotoxicity caused by azoxystrobin, which is found in Amistar, as well as Extra granules. In this work, we evaluated the significance of this damage in terms of yield in a cultivar that is particularly sensitive to phytotoxicity, as well as ways to minimize this damage.
We examined the Ramiro-type pepper cv. Madonna, which is sensitive to drench-applied material. We observed leaves yellowing and dropping off of the plants and a decreased rate of growth that persisted for about a month after the last drench. In terms of yield, we observed a delay in harvests throughout March, but there was no effect on overall yield, fruit size or fruit quality. Distributing the same total amount of fungicide across a greater number of application treatments (with a lower application rate) did not decrease the signs of phytotoxicity on the plants. In an accompanying experiment in line 4833 grown using a Spanish trellis system, we observed signs of phytotoxicity at the shoot meristems following the application of azoxystrobin. However, in that experiment, the fungicide treatment did not affect the rate of yield accumulation or overall yield. It is possible that the relatively high level of phytotoxicity observed in cv. Madonna is related to the use of a Dutch trellising system, in which the majority of the material reaches one shoot meristem of each plant as opposed to multiple meristems in the Spanish trellising system.
To date, we have not observed any phytotoxicity problems for the triazoles, such as Hosen. The other products permitted for use as drenches to control powdery mildew of pepper are Amistar and similar fungicides, which are strobilurins and Extra granules, which contain a triazole (Atemi) and a strobilurin (azoxystrobin). We recommend that growers who apply fungicide drenches continue to apply two drenches each season with chemicals from different families, except perhaps in particularly sensitive cultivars. This will significantly decrease the risk of fungicide resistance, ensuring the usefulness of this method for many years to come.
We thank the Plant Board for their financial support of this work.
מלות מפתח Capsicum
מחבר Shimon Pivonia, Rachel Levite, Ami Maduel
תאריך יצירה 14/3/2012
תאריך עדכון 14/3/2012