Association of Spring Pruning Practices with Severity of Powdery Mildew and Downy Mildew on Hop

Abstract

spring pruning practices with severity of powdery mildew and downy mildew on hop. Plant Dis. 96:1343-1351.Downy mildew (caused by Pseudoperonospora liumuli) and powdery mildew (caused by Podosphaera macularis) are important diseases of hop in the Pacific Northwest United States, and cultural practices may affect the severity of both diseases. The association of spring pruning quality and timing with severity of downy mildew and powdery mildew was assessed through analysis of survey data collected from commercial hop yards in Oregon and Washington. Among 149 hop yards surveyed, the most common pruning method was chemical desiccation (48% of yards), mechanical pruning (23%), or a combination of these practices (15%). The quality of pruning was assessed using a threecategory ordinal scale ("excellent", "moderate", or "poor") based on the amount of foliage remaining on plants following pruning. Excellent pruning quality was attained more often in yards pruned twice (74.6 to 82.1 % of yards) versus once (33.8% of yards), independent of pruning method. Seasonal severity of downy mildew in Oregon increased approximately twofold with reduction in pruning quality from excellent to moderate to poor. Pruning quality was not significantly related to levels of powdery mildew on leaves or cones in Oregon. Under more severe disease pressure in Washington, however, seasonal severity of powdery mildew on leaves and the incidence of cones with powdery mildew were significantly greater in yards that had poor pruning compared with excellent pruning. Moreover, yards that had excellent pruning quality received, on average, 1.1 to 1.5 fewer fungicide applications per season for downy mildew or powdery mildew compared with yards that had moderate or poor pruning quahty. This savings was associated with delayed initiation of the first application by 7.5 to 14.2 days in yards with excellent pruning quality. Replicated experiments in commercial yards in Oregon quantified the effect of delaying pruning timing 5 to 21 days compared with growers' standard practices on the diseases and yield. Downy mildew suppression by delayed pruning was dependent on cultivar and year of sampling, being significantly reduced fivefold only in 'Willamette' in 2007. Severity of powdery mildew and cone yield was similar between plots that received the delayed or standard pruning timing treatments. Collectively, these studies emphasize that early spring sanitation measures are associated with reduced primary inoculum and are critically important for managing both downy mildew and powdery mildew. A savings of at least one fungicide application per year appears achievable when spring pruning is conducted thoroughly and slightly delayed compared with growers' current practices.Cultural disease management practices are actions that involve the manipulation of the plant, its components, crop refuse, and the environment to reduce or prevent disease (5,26,31,34). In hop (Humulus lupulus L.), cultural practices are an important component of integrated management of the t...

Meta-Analysis Reveals a Critical Period for Management of Powdery Mildew on Hop Cones

“…The impact of midseason foliar disease levels and interactions of those foliar disease levels with quinoxyfen efficacy when applied during early cone development supports previous reports that seasonlong disease management is essential to reduce inoculum pressure and maintain acceptable disease levels at harvest (9,36). Based on the present results, even if relatively effective control strategies are applied to cones, high inoculum pressure (resulting from high disease levels on leaves) may still lead to unacceptable levels of disease on cones.…”

Concepts of Sustainability, Motivations for Pest Management Approaches, and Implications for Communicating Change

“…3). These pests occur in both Oregon and Washington, although pest incidence and damage to hops differ between the two states due to climate, cultivars produced in each state, and certain cultural practices such as irrigation methods and spring pruning (19,20). In Oregon, the mild, wetter climate generally favors downy mildew and hop aphid in most seasons.…”

“…These pests are less problematic in Washington (e.g., 26). Powdery mildew and spider mites occur in Oregon, and may be damaging, although they tend to be more problematic in the semi-arid climate of central Washington (e.g., 19,20). Based on pest management surveys (described below), on average farmers in Oregon reported 1.9 insecticide applications and 1.4 miticide applications per season.…”

Identification and distribution of mating‐type idiomorphs in populations of Podosphaera macularis and development of chasmothecia of the fungus

“…Because the ascigerious stage of the pathogen is absent, primary inoculum of P. macularis can be substantially reduced in the Pacific Northwest through spring pruning of hop plants to destroy the emerging flag shoots, either by mechanical or chemical means (Gent et al ., ). The absence of ascosporic inoculum in the Pacific Northwest greatly simplifies the management programme compared to other regions where both flag shoots and ascosporic inoculum may occur.…”

“…In addition, the research presented here has provided information that has resulted in changes in quarantine regulations by the state departments of agriculture in Washington, Oregon and Idaho to reduce the likelihood of the introduction of the second mating type of P. macularis . It is thought that the presence of the second mating type and the ascigerious stage would substantially increase seasonal carryover of inoculum and decrease the effectiveness of current management strategies for powdery mildew (Gent et al ., ). Long term, the presence of the ascigerious stage would undoubtedly change the diversity of the population of P. macularis found in the Pacific Northwest.…”