Issue link: http://read.dmtmag.com/i/108963
USE ONCE per season S treptomycin was a good antibiotic in the Pacific Northwest until resistance became a problem in Washington and Oregon orchards in the late 1980s. At one point, up to 100 percent of the isolates collected from some orchards showed resistance when analyzed in the laboratory. But more recently, according to Dr. Ken Johnson of Oregon State University, isolates have shown much lower resistance levels���only around 35 percent of the isolates collected in the two states now show resistance. ���We���ve shifted from saying ���don���t use it��� to ���use it one time per season,������ he said of the antibiotic streptomycin. ���Based on the new numbers, you can probably use it once per season, but you should mix it with a full rate of oxytetracycline at the same time to keep resistance low.��� ���M. Hansen compound. Johnson likens it to oxytetracycline, but says the biological has a shorter life than oxytetracycline. ���It has a better fit in an organic program or as a resistance management strategy than it does as a stand-alone product,��� he said. ���The problem with Serenade is that you have to double-down on applications because of its short life.��� Antibiotics (streptomycin, oxytetracycline, kasugamycin), applied at early bloom. Oxytetracycline has been the bread-and-butter product in the Northwest, but it���s not a strong performer, averaging about 60 percent disease incidence in trials, and timing has be just right. However, ���it���s the best thing we have,��� Johnson said, although it doesn���t match up to the old days of using streptomycin, before there was resistance. In trials comparing applications of Kasumin and oxytetracycline to streptomycin or oxytetracycline alone, Kasumin performed well, showing less than 15 percent disease incidence. To avoid the possibility of developing resistance with Kasumin, he recommends using a full rate of Kasumin with a quarter-rate of oxytetracycline. But Kasumin has not performed as well in eastern United States, he said, adding that streptomycin has done best there in efficacy trials. ���If you don���t have streptomycin resistance, it���s been the most effective antibiotic for eastern United States.��� A caveat for using Kasumin is phytotoxicity potential. Burning of the leaves has been observed a few times during residue trials on Granny Smith apples. ���It���s a warning that there could be finish problems with pears,��� he said. Soluble coppers (Phyton 27AG and Previsto), intended as bloom and petal fall treatments. The new soluble coppers are safer than the old fixed coppers and have a longer residual time of seven to ten days, compared to three days from antibiotics. Other advantages are good absorption by the plant and the ability to apply at late bloom. Also, the coppers are bactericidal (bacteria-killing), whereas the antibiotics are bacteriostatic (bacteria-inhibiting). He believes the soluble coppers may have a fit for some orchards, including organic orchards (components of the Previsto formulation have been accepted as organic). Extensive fruit finish testing of Previsto has not shown any problems. Phyton 27AG, copper sulfate in tannic acid, is registered, though fruit finish testing has not been completed, and the product���s organic status is unknown. The soluble coppers have shown a dose-response in research trials, and appear to give the best control of fireblight at around 96 ounces per acre. ��� 10 FEBRUARY 15, 2013 GOOD FRUIT GROWER www.goodfruit.com