Trials were conducted in orchards near Chico, CA and microplots near Parlier, CA to examine symptoms and control measures for a replant disease (RD) on almond (Prunus dulcis). In the orchard trials, areas with a recent history of severe RD were cleared, given soil fumigation treatments in the fall, and replanted with almond trees on various rootstocks the following winter. The replants in nonfumigated soil developed severe RD (stunting, wilting, chlorosis, defoliation) by the following summer, while those in most fumigated treatments remained healthy. Trees in nonfumigated soil developed smaller trunk diameters and fewer healthy roots ≤1 mm diameter, compared with the healthy trees. Almond developed RD on all rootstocks evaluated (Marianna 2624, Lovell, and Nemaguard), but the trees on Marianna 2624 were the most severely affected. Pre-plant tree-site (spot) fumigation treatments with methyl bromide (MB), chloropicrin (CP), 1,3-dichloropropene (1,3-D), 1,3-D + CP, iodomethane, and iodomethane + CP all prevented severe RD. Broadcast soil fumigation with CP also was effective, but broadcast MB and 1,3-D were ineffective. In microplots filled with RD-conducive soil, CP was more potent than MB for prevention of RD on Nemaguard peach. There was no association between nematodes and RD in orchard or microplot trials. The RD apparently was mediated by a biological agent(s) other than nematodes and can be prevented by appropriate fumigation with CP or other MB alternatives.

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Young almond (Prunus dulcis, cvs Carmel, Peerless and Price) orchards established on the plum rootstock Marianna 2624 (P. cermifera X P. munsoniana) contained trees that exhibited poor terminal shoot growth and wilted, chlorotic leaves. The scion/rootstock graft union showed an external splitting of the bark and an internal line of necrotic bark tissues that extended into the woody cylinder of the union, which was deeply pitted. Affected trees declined. The disease was named almond brown line and decline (ABLD). Incidence of ABLD ranged up to 55% per cultivar in some orchards. Numerous attempts to graft-transmit orchard collections of ABLD to healthy almond/h.larianna 2624 indicators failed. Also, ABLD does not appear to be soil-borne. However, ABLD was serendipitiously determined to be bud-perpetuated when infected scion buds from an apparently healthy appearing Peerless almond/peach tree located in a foundation orchard were grafted onto healthy rooted cuttings of Marianna 2624 to produce yearling trees. Also, graft-inoculations on the almond scion portion of healthy trees, but not the plum rootstock portion, with the peach yellow leafroll mycoplasma-like organism (PYLR-MLO) caused symptoms resembling ABLD. Laboratory and glasshouse assays of several symptomatic trees did not detect tomato ringspot virus and two ilarviruses. These results suggest that an MLO, possibly PYLR-MLO, may be the causal agent of ABLD and that Marianna 2624 is probably resistant to the PYLR-MLO.

Recent reports of a preharvest rind disorder of Satsuma mandarin fruit resulted in severe crop losses in some growing areas of California (Butte, Fresno, Tulare, and Kern Counties). Symptoms were more frequently observed on fruit on the outer perimeter of the tree and on the exposed side of the fruit. Fungal isolations from affected fruit were inconsistent among orchard sites and growing seasons. Isolations resulted in species of Alternaria, Fusarium, Macrophomina, Ulocladium, and Cladosporium. In laboratory studies, mandarin fruit that were soaked in water for 6 h at 15 to 35°C, air dried, and incubated at 20°C for 3 days developed lesions similar to those observed in the field. When fruit were treated with an agricultural summer spray oil or the antitranspirant di-1-p-menthene prior to water soaking, the incidence and severity of the disorder were significantly reduced. Similar results were obtained in 2 years of field trials at two sites using one to three preharvest applications with the agricultural antitranspirant or summer oil starting after fruit color break. In most trials, a single application of these treatments at 1 or 2 weeks after color break was highly effective. Fungicides were inconsistent in their efficacy, whereas trees that were physically protected from rain did not develop the disorder. These data suggest that this mandarin rind disorder is a physiological, abiotic disorder rather than a pathological problem caused by fungi and can be economically managed with water-repellant treatments.

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