Figure 1. Botrytis fruit rot often starts beneath the calyx where moisture can get trapped, along with petals, where it will persist long enough for the pathogen to germinate and infect the fruit. (photo by G. J. Holmes) A recently published paper in Phytopathology by Naegele et al. adds to the work done by Cosseboom … Continue reading New publication confirms trends in fungicide resistance

In the California strawberry industry, it's widely accepted that there are four major diseases caused by soilborne pathogens: Macrophomina root rot (caused by Macrophomina phaseolina) (Fig. 1), Fusarium wilt (caused by Fusarium oxysporum f. sp. fragariae), Verticillium wilt (caused by Verticillium dahliae), and Phytophthora crown and root rot (caused by Phytophthora spp.). Figure 1. Example of … Continue reading Which soilborne pathogens are most common in California strawberry fields? Part 1 – Watsonville/Salinas district

Some strawberry varieties are genetically resistant to the Fusarium wilt disease. For example, Fronteras, Portola, and San Andreas are Fusarium wilt-resistant varieties from the University of California. A description of disease resistance for currently available varieties is on the California Strawberry Commission web site. All Fusarium wilt-resistant varieties have the same resistance gene, called “FW1”. Until … Continue reading FW1-resistant varieties with Fusarium wilt in Oxnard, CA

A recent publication by Mello et al. reports that strawberry powdery mildew (SPM) was reduced by nighttime application of UV-C to field plots at 200 J m-2 . Disease reduction was equivalent to that provided by weekly fungicide applications in CA and superior to that provided by twice weekly fungicide applications in FL.  No negative … Continue reading New publication reports efficacy of UV-C against powdery mildew in FL and CA

Figure 1. A grower field affected by Macrophomina crown rot. About the plant disease diagnostic service Soil-borne pathogens such as Macrophomina phaseolina are challenging strawberry production as they become increasingly prevalent across California (Fig. 1). Accurate disease diagnosis is the cornerstone of integrated pest management. The Strawberry Center's disease diagnostic service has been serving California … Continue reading Cal Poly Strawberry Center Disease Diagnostic Service

We usually see Zythia leaf blotch (caused by Zythia fragariae) during the early spring when plants are small and the weather is cool and wet. With summer planting in Santa Maria occurring in May, especially in fields close to the coastline where fog and heavy dews are common, the same conditions exist (i.e., small plants … Continue reading Off-cycle Zythia leaf blotch

In the vast majority of seasons, powdery mildew (PM) (caused by Podosphaera aphanis) is the most economically important foliar disease of strawberries in California. Many growers have observed that PM is particularly destructive in glasshouses and under plastic tunnels. This could be due to the difference in temperature and relative humidity or to filtering UV … Continue reading Tunnel plastics, UV and powdery mildew

A new publication by Baggio et al. (2022) out of the University of Florida provides evidence that 1,3-dichloropropene (1,3-D) alone and in mixture with chloropicrin were more effective in reducing inoculum of Macrophomina phaseolina than chloropicrin alone. We generally think of 1,3-D (known under the trade name TELONETM) as an effective nematicide with minor efficacy … Continue reading New research shows 1,3-D is effective against Macrophomina

Do you know how to diagnose root-knot nematode in strawberry? We recently came across a rare occurrence of root-knot nematodes in two samples submitted to the Strawberry Center's Disease Diagnostic service. The samples were both from the Santa Maria district and were both positive for root-knot nematodes (Meloidogyne spp.). The species most commonly associated with … Continue reading Root-Knot Nematode in Strawberry

Figure 1. Rhizopus rot is diagnosed by the conspicuous sporulation on the fruit surface. Under high humidity, sporulation appears "hairy" but is more appressed under drier conditions. Rot progresses very quickly and fruit become liquified within a couple of days. (photo by G. Holmes) June is here and temperatures are rising. Along with rising temperatures … Continue reading Rhizopus rot or “leak”

It's helpful to look at similar systems to learn more about your own. For example, we can learn a lot about Macrophomina in strawberries by looking at the diseases this fungus causes in many other crops where it has been studied more intensively. A recent paper in the journal Plant Disease reviews dry root rot … Continue reading What can we learn from Macrophomina in chickpea?

Figure 1. Greenhouse-grown strawberry leaf showing a few powdery mildew lesions. The results of two powdery mildew fungicide trials conducted in 2021 were just published in Plant Disease Management Reports. In these trials, 17 unique products were evaluated for performance against powdery mildew under greenhouse conditions (Fig. 1). Weekly disease incidence and severity was assessed … Continue reading JUST PUBLISHED: Fungicide performance against powdery mildew, 2021

Strawberry powdery mildew caused by Podosphaera aphanis, is an important disease in California strawberries (Fig. 1). Strawberry Center master's student Michael Palmer recently published his work on fungicide resistance in the journal Plant Disease (https://doi.org/10.1094/PDIS-12-20-2604-RE). Because P. aphanis is an "obligate parasite" all of the experiments were done using live plant tissue (Fig. 2). This … Continue reading RECENTLY PUBLISHED: Fungicide resistance in strawberry powdery mildew in California

Figure 1. Botrytis fruit rot (gray mold) showing typical gray sporulation beginning under the calyx and spreading towards the tip. A lot of people never heard the word "epidemic" (the rapid spread of a disease), "pandemic" (spread of a disease over a wide area) or "epidemiology" (the study of how disease spreads) until the COVID … Continue reading Classic Botrytis data from 1987

The results of two fungicide trials conducted in 2021 were just published in Plant Disease Management Reports. In these trials, 20 unique products were evaluated for performance against Botrytis fruit rot (Fig. 1). After 5 applications (Fig. 2), fruit were evaluated in the field (at-harvest) and postharvest after storage at room temperature for 10 days. … Continue reading JUST PUBLISHED: Fungicide performance against Botrytis fruit rot 2021

Figure 1. Mild bronzing caused by frost on white fruit of cultivar Monterey. This level of bronzing will be harder to detect when the fruit turns red. In my last post, I showed a bunch of photos of frost injury. Later I noticed another effect: Bronzing (Figs. 1, 2 & 3). Just like misshapen fruit … Continue reading Bronzing caused by frost

Here's an update on the Cal Poly Strawberry Center’s Disease Diagnostics. A total of 16 samples have been submitted so far of which 11 have been diagnosed with the pathogens in (see Table below). Relative to this time last year we are seeing more samples positive for Phytophthora spp. and Pythium spp. These two soil-borne … Continue reading Disease diagnostic lab updates

Recent frosts at the Cal Poly farm has brought frost injury in all its variety. According to the Compendium of Strawberry Diseases "frost injury is probably the most common non-pathogen related and non-insect-related disorder affecting strawberry flowers and fruit." Whenever temperatures dip to below freezing, expect to see a variety of deformed fruit and blackened … Continue reading Frost injury

The author (Michael Palmer) in a strawberry field in Santa Maria, CA. Photo by G. J. Holmes Michael Palmer finished his master's thesis last winter and his second paper just appeared in the journal Plant Health Progress (https://doi.org/10.1094/PHP-12-20-0101-RS). This paper works out the methods for screening strawberry cultivars for their susceptibility to powdery mildew caused … Continue reading JUST PUBLISHED: Strawberry host plant resistance to powdery mildew