The growing season has kicked into high gear, and orchardists are monitoring their pest and disease situations closely, continuing to scout orchards and to utilize cultivation practices, reducing their reliance on crop sprays. But in many growing regions, tree fruit requires a spray program, whether that program is a conventional or an organic one. To meet the demands of the blemish-free retail market, or to protect fruit trees from serious pest and disease threats, spraying tree fruits remains a reality for many commercial growers.
“Depending on the location, growers have to use some kind of chemical intervention every season, whether it is conventional or organic, due to the disease pressures encountered from environmental conditions,” Kari Peter, assistant professor and research associate, Tree Fruit Pathology, Penn State Fruit Research and Extension Center, said. “Also, the most popular varieties of apples grown and in demand are quite susceptible to many diseases. This is especially true for folks who grow fruit in the eastern half of the United States.”
To make the most of the applied protectants, proper selection, timing, and application is a necessity. Overlooking any one of these factors can mean product ineffectiveness and crop loss. By monitoring disease conditions closely, growers can best select the products and efficacies needed for the actual pest pressure occurring in their orchards.
“If there was just one thing I could make growers improve, it would be to not stretch their spray intervals too much,” Peter said.
That’s because there are critical windows of opportunity for controlling many disease concerns. Missing those windows means sacrificing control and increasing the amount of damaged crop. For some of the most economically important diseases of tree fruit, timing really is everything.
“For certain diseases, such as apple scab, getting control of the disease early in the season is critical,” Peter said. “The overwintering spores wreak the most havoc during mild, rainy periods from green tip through about mid-June, so protection with fungicide during this period is very important.”
Bloom time is another critical period, particularly for fire blight. Conditions during apple bloom, particularly when warm temperatures are combined with moisture, will require that precautions are taken to prevent this disease. Streptomycin, an antibiotic, applied directly to the blossoms can protect trees from infection.
If this opportunity is missed, and “blossoms become blighted, the disease can spread very quickly in a susceptible orchard, and young trees are at risk of potentially dying,” Peter cautioned.
While pesticide training is mandated for all growers, often common sense, beyond the strict adherence to proper safety procedures and the use of all products as per their label information, is needed. For example, copper mixtures, when combined with certain other additives and slow-drying conditions due to the weather, can have their phytotoxic properties enhanced. Realizing this, and limiting the propensity for problems, requires proper planning.
“Copper is excellent for managing bacterial spot on peach; however, it will cause some phytotoxicity. Consequently, care must be taken when applying copper sprays,” Peter said. “There have been problems when growers have overlooked these critical issues and serious damage occurred to trees.”
Another serious concern plaguing the industry is fungicide resistance. Broad spectrum fungicides, rather than those that target a limited number of species, carry a lower risk for developing resistance and are more likely to maintain their effectiveness in fighting disease.
Because of the prevalence of resistant fungicides, every fungicide must now have a Fungicide Resistance Action Committee, or FRAC, group code that indicates its mode of action. The 2017 updated list is available on FRAC’s website.
“When it comes to managing fungal diseases in particular, fungicide resistance is the biggest concern. When growers focus on ‘spraying by the numbers,’ and alternate sprays by the FRAC group codes,” the chance of pests developing resistance is greatly decreased, Peter said. “This is their best strategy for helping to maintain the efficacy of certain fungicides.”
Other chemicals, such as antibiotics and insecticides, also can cause resistance, rendering them ineffective against the targeted disease-causing pathogen. The International Resistance Action Committee (IRAC) has a list of modes of action of various insecticides available, and growers should rotate groups.
Rotating chemicals requires more than a different product: it requires products with different modes of action, as well as limiting sprays of products within the same FRAC or IRAC code group per season. New products can cause confusion, with many of those most effective for a given problem having the same FRAC codes. And as chemicals evolve, a plethora of new products can make older ones obsolete.
Applying the correct amount and strength of the appropriate chemical, and applying it everywhere it needs to go, at the time it needs to get there, makes for an effective spray program. If equipment isn’t correctly calibrated, or chemicals aren’t properly mixed in the first place, results will vary.
“Calibration and maintenance of sprayers is very important,” Peter said. “Regardless of what kind of a product a grower may be applying, coverage of trees is of the utmost importance. If a sprayer is not calibrated correctly, growers may run into the problem of not protecting their trees adequately, such that disease could occur on the top of the trees, if the sprayer is not reaching that height.”
Record-keeping tools, such as one found on the Penn State Extension website are required, and serve to help safely and effectively make chemical spray selections throughout the season. Re-entry times after spraying can’t be overlooked, nor can the time required between spraying and crop harvest. Penn State Extension, along with many other programs, offers detailed lists outlining these parameters for common orchard sprays.
“Although sprays are necessary, growers do use a variety of integrated pest management (IPM) methods in order to be sustainable, such as spraying when disease conditions are present, and practicing sanitation in the orchard by removing disease plant tissue, in order to limit disease pressure year-to-year,” Peter said.
With today’s focus on IPM, growers are relying less on chemical spray applications, choosing to treat orchards when environmental conditions and pest presence indicate an elevated concern for crop damage. When spraying is needed, knowing what, when and how to apply products in order to optimize their effectiveness is key to success.