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RaspberryBy, Lisa DeVetter (Washington State University), Tom Walters (Walters Ag Research), and Inga Zasada (USDA-ARS)

 

Washington State leads national production of processed red raspberry with a single county (Whatcom) responsible for 97 percent of in-state production. Growers in Whatcom County produced just over 68 million pounds of fruit in 2017 with raspberry production contributing to the vibrancy of the rural economy in northwestern Washington. Despite the scale and economic impact of the raspberry industry, a microscopic nematode poses a significant threat to growers.  This nematode is Pratylenchus penetrans, more commonly referred to as Root Lesion Nematode (RLN).

Root lesion nematode is a migratory endoparasitic nematode that spends its life in both the soil and plant roots. It is inside those fine roots where it feeds and causes damage leading to reductions in plant productivity, and in extreme cases, plant death.

Raspberry growers have struggled to successfully manage RLN since the phase out of methyl bromide. Fumigant alternatives to methyl bromide have been inconsistent and sometimes ineffective at controlling RLN. Furthermore, post-plant management options are limited and have not been shown to be very effective across a wide range of situations. Viable solutions for RLN management were needed by the raspberry industry to protect their high-value crop from this destructive nematode.

In response to growers’ needs, researchers teamed up across institutions with the goal of generating information and data-driven management practices that would allow growers to successfully manage RLN. This research started approximately eight years ago and the information generated now allows growers to manage RLN based on knowledge of RLN biology, at-planting population densities, soil type, and fumigant chemistry and application methods.

3BlackberryFusarium

By, Steven T. Koike, Director, TriCal Diagnostics and Tom Gordon, Professor, University of California at Davis

 

Introduction to Fusarium Wilt

Fusarium wilt diseases are well known problems that affect many crops and result in significant losses of yield and quality. In California’s central coast region, a number of Fusarium wilt diseases occur and affect crops such as celery, cilantro, lettuce, pepper, strawberry, and tomato (see Figure 1, column 3 for a list of some susceptible coastal crops).

Fusarium wilt diseases share a basic profile: (1) The pathogen can survive in the soil for a relatively long time, up to several years, without the presence of a susceptible crop; (2) In the presence of a susceptible plant, the Fusarium fungus penetrates the root, colonizes root tissue, enters the plant’s vascular tissue (xylem), and moves systemically into the plant stems via these vascular tubes; (3) Disease symptoms develop primarily due to the plugging up of the plant vascular tissue; (4) Symptoms include stunting and poor growth, yellowing of foliage, wilting of foliage, collapse of the plant, distinctive brown to red discoloration of the vascular tissue in roots and stems, and eventual death of the plant; (5) Because these pathogens are soilborne, Fusarium is readily spread in contaminated soil and crop residues that adhere to equipment and vehicles; (6) Fusarium wilt management is achieved by a combination of rotating to non-host crops, practicing field sanitation (avoid moving contaminated dirt on equipment), planting resistant cultivars, and in some cases applying pre-plant fumigants (example: conventional strawberry).

 Fusarium Fig1 Illustration

Fusarium wilt diseases are caused by one species of this fungus, Fusarium oxysporum. Researchers have shown that Fusarium wilt pathogens from different crops are genetically distinct from each other. A major implication of this genetic diversity is that each Fusarium wilt pathogen has a very narrow host range and usually causes disease on only one type of crop. The Fusarium wilt pathogen affecting celery causes disease in celery but does not cause symptoms in other crops such as lettuce or strawberry; the F. oxysporum that causes strawberry decline and death does so only to strawberry but not to lettuce or tomato. To help clarify this host specific phenomenon, plant pathologists give each Fusarium oxysporum pathogen the additional designation of “forma specialis” (abbreviated “f. sp.”) to indicate the host of that particular pathogen. The F. oxysporum that causes disease in celery becomes F. oxysporum f. sp. apii. Fusarium wilt of lettuce is caused by F. oxysporum f. sp. lactucae. See Figure 1, column 3 for a list of such designations for coastal crops. Pathogenic F. oxysporum in some cases can be further differentiated into distinct sub-populations such as races or somatic compatibility groups (Figure 1, column 4). These F. oxysporum pathogens persist in field soils for extended periods of time, thereby causing long-term concerns for a grower.

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USDA-ARS, Appalachian Fruit Research Station, Kearneysville, WV

One of the biggest challenges in strawberry production in the United States is managing diseases and pests. Diseases such as gray mold (caused by Botrytis cinerea), anthracnose (caused by Colletotrichum acutatum), or powdery mildew (caused by Podosphaera aphanis) can cause severe losses by reducing fruit quality and yield as well as causing fruit decay during production and after harvest, if not controlled beginning early on in the production cycle (Burlakoti et al., 2013; Carisse et al., 2013; Smith, 2013; Xiao et al., 2001). For control of gray mold and powdery mildew, it has been paramount that the control measures begin in the field at bloom, to protect flowers from infections (Figs. 1 and 2) that, in the case of gray mold, may account for up to 80 percent of fruit decay (Bulger et al., 1987).

 

Healthy (left), Botrytis cinerea (center) and Podosphaera aphanis-infected (right) strawberry flowers.

Fig. 1. Healthy (left), Botrytis cinerea (center) and Podosphaera aphanis-infected (right) strawberry flowers.

Fungicides traditionally have been used for controlling these diseases with regular applications from the early flowering stage through harvest (Bulger et al., 1987; Mertely et al., 2002; Wedge et al., 2007; Wilcox and Seem, 1994). However, their use has increasing limitations due to rapidly developing resistance to commonly used fungicides, new regulations limiting use of pesticides, especially in protective cultures, and growing demand for fruit free of pesticide residues (Wedge et al., 2007; Pokorny et al., 2016; Smith, 2013).

 Weeds

(originally published March/April 2018)

Weeds can be defined as plants growing out of place and can rapidly populate in ecosystems that do not support their natural enemies.  Many methods are being used to keep weeds under control. These include burning them, pulling them out or chopping them down, and treating them with herbicides.

Vegetable growers ranked weeds as number one obstacle to organic crop production. In early stages of crop growth, weeds compete at a faster rate than crop seeds for water, space, and nutrients especially in the first 20-30 days of crop growth. Organic growers have been using mechanical cultivation and hand weeding to control weeds. However, frequent soil cultivation decreases soil health and disrupts the ecological system; increases fuel and labor costs, and brings buried weed seeds to the soil surface. Biological control holds much promise for long-term, economical, and environmentally sensitive weed management.