Oxytetracycline for fire blight control: Use restrictions on the Mycoshield label
Oxytetracycline is an antibiotic used for controlling blossom blight. Growers should note that there are use restrictions on the label of one of the oxytetraycline formulations available in Michigan.
Oxytetracycline (OxyTc) is an antibiotic that is used for control of the blossom blight phase of fire blight. OxyTc is not as effective as streptomycin for blossom blight control in situations where streptomycin resistance is not present. OxyTc is also not as effective as Kasumin in controlling streptomycin-resistant strains of the fire blight pathogen. The best use for OxyTc is for blossom blight control under low to moderate disease pressure and also as an alternate material in a streptomycin resistance situation if a spray is needed following two consecutive Kasumin applications.
There are two OxyTc materials available in Michigan:
1) Mycoshield [NuFarm] is OxyTc Calcium complex, and
2) FireLine [AgroSource] is OxyTc hydrochloride.
The use rate of both materials is the same: 200 ppm or 1 lb per 100 gallons per acre. Also, both have a 60-day per-harvest interval. However, because OxyTc is a bacteriostatic material, it should not be used after bloom. While we have not compared these materials head-to-head for blossom blight control in Michigan, data from Ken Johnson at Oregon State University indicates that FireLine has slightly better efficacy than Mycoshield.
More importantly, there are two restrictions on the Mycoshield label stating:
1) “DO NOT use treated crop or byproducts for feed” and
2) “DO NOT allow livestock to graze on treated orchards.”
These restrictions are present only on the Mycoshield label and are not present on the FireLine label. Thus, if OxyTc is to be used for blossom blight control on processing apples in which apple pomace may be used for animal feed, use FireLine and DO NOT use Mycoshield. Also, carefully read either label prior to using these materials.