Fungi Associated with and Influence of Moisture on Development of Kernel Mold of Hazelnut.

Kernel mold on hazelnuts is defined by the United States Department of Agriculture, U.S.A., as any visible fungal growth either on the outside or inside of the kernel. Only one yeast and one filamentous fungus have been associated with kernel mold of hazelnut in Oregon. In this report, fungi were isolated from kernels with mold and identified using morphological and molecular characters. Penicillium spp. were isolated most often from kernels with mold, but species of Aspergillus and Cladosporium and Diaporthe rudis were also frequently isolated. Additional fungi from three other genera were also isolated. All of the same fungi were also isolated from symptomless kernels. Eremothecium coryli or Ramularia sp. previously associated with kernel defects in Oregon were not found associated with symptoms of kernel mold. Incidence of mold was the highest when nuts were incubated in moist chambers on wet, nonautoclaved orchard soil and was significantly higher than kernel mold found in nuts incubated on either air-dried soil or wet, autoclaved soil. Preventing hazelnuts from coming in contact with wet soil in the field using elevated wire screens resulted in significantly less mold development in two out of three years evaluated. Nuts on screens had a greater chance to dry out between rainstorms as measured by significantly lower nut moisture levels at harvest.

Tank Mixing Fungicides for Effectiveness Against Eastern Filbert Blight of Hazelnut.

Hazelnut (Corylus avellana) production in Oregon primarily occurs on cultivars susceptible to Anisogramma anomala, the causal agent of eastern filbert blight (EFB). Management of EFB involves planting resistant cultivars, removal of cankered limbs, and the application of fungicides. Tank mixes of demethylation-inhibiting (DMI; Fungicide Resistance Action Committee [FRAC] group 3) or quinone outside inhibitor (QoI; FRAC group 11) fungicides with chlorothalonil (FRAC group M5) at full or reduced rates were evaluated for effectiveness against A. anomala. The use of chlorothalonil in a mix with a DMI or QoI fungicide was an effective treatment for EFB even if each component of the mix was at half the labeled rate. Different liquid or dry formulations of chlorothalonil were equally effective in a tank mix for EFB control. The combination of propiconazole (FRAC group 3) tank mixed with trifloxystrobin (FRAC group 11) was not effective, whereas trees treated with propiconazole tank mixed with pyraclostrobin (FRAC group 11) resulted in significantly fewer EFB cankers compared with nontreated trees. When using tank mixes for EFB management, DMI fungicides should remain at full rates while mixing with a half-rate of chlorothalonil. In contrast, QoI fungicides and chlorothalonil could both be used at half-rates and still maintain acceptable EFB control. Tank mixing chlorothalonil with fungicides at risk of resistance development can help maintain consistent EFB control and should help prevent or delay the emergence of fungicide-resistant A. anomala isolates.

Evaluation of Quinone Outside and Succinate Dehydrogenase Inhibitors for Effectiveness Against Eastern Filbert Blight of Hazelnut.

Most of the hazelnut production in Oregon, a value of $130 million in 2014, was based on eastern filbert blight (EFB) susceptible cultivars. On these cultivars, EFB management involves, among other tactics, fungicide treatment during bud break and early shoot growth. Many active ingredients have been shown to be effective against EFB. This report summarizes the evaluation of quinone outside (QoI, FRAC group 11) and succinate dehydrogenase (SDHI, FRAC group 7) inhibitors alone and in combination with each other or with demethylation-inhibiting (DMI, FRAC group 3) fungicides for management of EFB. Based on a meta-analysis, picoxystrobin, pyraclostrobin, or trifloxystrobin alone resulted in significant control over nontreated trees ranging between 64 and 74%. Fluoxastrobin was not as effective as other QoI fungicides with an average of 44% control and high variability. SDHI fungicides as a group were less useful for management of EFB with boscalid, fluopyram, and penthiopyrad ineffective while fluxapyroxad averaged 83% control against EFB. Prepackaged mixes of QoI materials with either SDHI or DMI fungicides were also significantly effective against EFB. Use of QoI fungicides and the SDHI material fluxapyroxad offers added flexibility and complexity within EFB management programs. Growers can incorporate any of five different modes of action in EFB management programs including FRAC groups M1, M5, 3, 7, and 11.

Disease Incidence and Ascospore Dispersal from Cut Hazelnut Branches Colonized by Anisogramma anomala.

Hazelnut branches bearing stromata of Anisogramma anomala cut in December (2009 and 2010) were compared with branches cut prior to bud break in March to investigate these sources of inoculum. Branches were placed into brush piles (sources). Spore traps and potted hazelnut trees were placed adjacent to each source, 6.4 m upwind and downwind, and 20 m downwind from each source. Significantly more ascospores were detected near sources of branches cut in March compared with December in 2010 however, no differences were detected between pruning treatments in 2011. Ascospore viability, as assessed by trypan blue stain, averaged 50% for both pruning times each season. Significantly more ascospores were detected 6.4 m downwind compared with 6.4 m upwind or 20 m downwind of a source both years. All potted trees exposed to branches from both pruning treatments within sources became diseased both years. The proportion of potted trees that became infected was greater for the downwind group than the upwind for both years, suggesting that ascospores were dispersed beyond the rain splash dispersal range of sources. Ascospores from diseased branches pruned in December or March remained viable, infectious and were dispersed at least 20 m downwind.