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  • Author or Editor: Dean R. Evert x
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Abstract

Rickettsia-like bacteria (RLB) are the presumptive cause of phony peach disease and are most numerous in peach (Prunus persica (L.) Batsch) roots. Of apparently healthy peach trees in a heavily infected orchard, 54% had RLB in root samples evaluated by 400 × phase contrast microscopy. Removing all peach trees with visible symptoms of phony peach disease would minimize the number of trees in the orchard infected with RLB. Of trees visibly infected with phony peach disease, 8% had root samples free of RLB on both sampling dates. Leaf concentrations of Mg and B varied significantly (P < 0.7%) with RLB levels in peach roots on 3 of 4 sampling dates. No element tested (P = 5%) separated roots free of RLB on two sampling dates from roots averaging 1 to 9 RLB per microscope field on one date and free of RLB on another date. RLB in peach roots preceded development of visible symptoms of phony peach and changes in leaf elemental concentrations. Soil analysis did not identify RLB infected tree roots (P = 5%).

Open Access

Bahiagrass (Paspalum notatum Flugge cv. Paraguayan-22) growing under newly planted peach [Prunus persica (L.) Batsch.] trees severely stunted the trees. Neither supplemental fertilizer nor irrigating with two 3.8-liters·hour-1 emitters per tree eliminated tree stunting emitters were controlled by an automatic tensiometer set to maintain 3 kpa at a depth of 0.5 m under a tree in bahiagrass. Preplant fumigation with ethylene dibromide at 100 liters·ha-1 increased tree growth, but not tree survival. Fenamiphos, a nematicide, applied under the trees each spring and fall at a rate of 11 kg-ha -1 had no positive effect on tree survival, tree growth, or nematode populations. Bahiagrass tended to suppress populations of Meloidogyne spp. under the trees., Meloidogyne spp. were the only nematodes present that had mean populations > 65 per 150 cm3 of soil. Leaf concentrations of several elements differed between trees growing in bahiagrass sod and in. bare ground treated with herbicides. Leaf Ca was low for all treatments in spite of a soil pH near 6.5 and adequate soil Ca. The severe stunting of trees grown in bahiagrass, irrespective of the other treatments, demonstrated that bahiagrass should not be grown under newly planted trees. The low populations of parasitic nematodes in bahiagrass showed that bahiagrass has potential as a preplant biological control of nematodes harmful to peach trees. Chemical name used: ethyl 3-methy1-4-(methylthio) phenyl (1-methylethyl) phosphoramidate (fenamiphos).

Free access

Abstract

The electrolytic, visual, and electrical impedance methods for estimating freezing injury were highly associated. The electrolytic method was more closely associated with the visual method and better separated the effects of freezing temperatures than did the electrical impedance method. The electrical impedance method yielded results in the shortest time. The electrical impedance and visual methods evaluated freezing injury to woody internodal stem sections without the need for unfrozen controls.

Open Access