High Humidity = Bad Hair Days and Brown Rot.
Heavy morning dew and thick air make some summer days at our Ozark orchard–long. Sticky oppressiveness not only signals peach season but also Monilinia fruticola, a vicious fungus that destroys stone fruit. Wanting warm and wet conditions, brown rot thrives in rainy periods with degree days above 70 when precipitation and wind speed the spread of fungus spores. Peaches and nectarines are under particularly intense pressure from brown rot. The ideal moist and lush environment develops as fruit ripens and softens in too much condensation, and multiplying fungus spores quickly rot crops before, during, and after harvest. Split pits caused by high rainfall and infection dispersed by feeding Japanese and Green June Beetles further advance decay. Yuck.
Our first and best defense against brown rot is good cultural practices. Because we are an integrated pest management (IPM) orchard, we coordinate several tactics so that we can grow fruit without relying excessively on synthetic pesticides. Sitting high on a ridge, our orchard site is valuable. Young buds have favorable protection against spring frost and trees have improved air circulation in summer humidity. The more open the canopy, the better the air flow, allowing leaves and fruit to dry faster after rain or dew. Both dormant pruning and summer pruning also help create this openness and ensure removal of any diseased fruit and branches. Scheduled thinning is another critical step against brown rot and other pests. Late winter into early spring, we reduce peach and nectarine crops by hand prior to pit-hardening to prevent thinned fruit from maturing to the point that fungus spores can colonize. Eliminating such sources of brown rot stops the most avoidable escalation. Additionally, substituting cover crops for synthetic fertilizers balances nutrition, making trees fitter when insects and diseases assault.
Regular scouting–several times per day even–alerts us to pest damage so that we can promptly decide what if any action to take. Typically, maintaining sound IPM cultural measures lessens dependence on synthetic pesticides. In a summer growing season with low humidity and low rainfall, our orchard might use a fungicide on a 14- to 20-day cycle versus a 7- to 10-day cycle. This reduced spray program is possible only if assimilated with active scouting and solid overall pest management methodology, especially in an Ozark climate that puts fierce disease and insect stress on fruit. Weather determines the severity of this pressure. In a summer growing season with high humidity and high rainfall, fungicides protect fruit crops from rotting. Timing and targeting are key. To minimize potential harm to anything but the target pest, we time a control carefully. To ensure a control is specific to its target pest, we use the minimal amount of material required to effectively prevent disease. Applying an appropriate fungicide mixture early in the morning on a light breeze day, for instance, is more prudent than administering a too potent application in the afternoon on a windy day.*
Moments when the weather will not cooperate and the beetles are too successful can make us pause and wonder how many more seasons are reasonable. Safeguarding native habitat as well as orchard habitat urges us to brave the elements a bit longer, and raising there-are-no-words-to-describe-our-delicious-local-fruit begs us to share. Plus, we deserve some sunshine.
*Mitigating pesticide exposure is out of a concern for our neighbors, ourselves, our dogs, and our wild. A diluted fenbuconazole solution arrests brown rot in our orchard and poses a lesser threat to bees. We continually research and evaluate our controls, working toward as sustainable an orchard system as possible in our climate. Thanks to our entomology friends Dr. Donn Johnson and Research Assistant Barbara Lewis at the University of Arkansas for their many years of effort and to Tree Fruit Research Entomologist Dr. David Biddinger at Penn State for his extensive push to protect pollinators.