Cal Poly Strawberry Center Disease Diagnostic Service

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 strawberry growers since its inception in 2014. This diagnostic service, fully funded by the California Strawberry Commission, is free to all California strawberry growers, pest control advisors, breeding programs, and industry partners. Diseased strawberry plant samples are self-collected and submitted to the Strawberry Center for disease diagnosis. As part of their participation in the Strawberry Academy, Cal Poly student assistants process submitted plant samples, gaining valuable pathology laboratory experience and training.

Sample submission

If you haven’t submitted a sample before and plan to submit one, please go over these resources on sampling and sample submission first.

How to take a representative sample

How to submit us a sample

When you are ready to submit a sample, please fill out the sample submission form to the best of your knowledge and submit the completed form along with the sample. You can drop off samples at the Strawberry Center or Strawberry Pathology Lab (Cal Poly campus, Building 11, room 106).

It is also helpful to us in our diagnostic process if photos of diseased plants in the field can be emailed to Dr. Shashika Hewavitharana @

Figure 2. Plant sample submitted to the Cal Poly disease diagnostic service.

Our diagnostic process involves the following steps: (1) Inspect unaltered plant sample(s) (Fig. 2) and crown tissue (Fig. 3) for symptoms and signs of disease; (2) Isolate pathogens using artificial media (Fig. 4); (3) Observe morphology using microscopy; and (4) Detect them using molecular methods such as polymerase chain reaction (PCR), quantitative PCR, recombinase polymerase amplification and immunological methods. Finally, you will receive within 1-2 weeks a diagnostics report with the results.

Figure 3. Crown symptoms of a submitted sample.
Figure 4. Verticillium dahliae isolated on a semi-selective media called NP-10.

By September 1, 2022, we received 120 samples in total from all three districts and nurseries (Fig. 5).

Figure 5. Number of samples submitted from each strawberry production district and nurseries.

Among the four major soil-borne pathogens Macrophomina phaseolina was the most prevalent followed by Phytophthora spp. Interestingly, we found 4 samples positive for Meloidogyne hapla (Northern root-knot nematode) (Fig. 6).

Figure 6. Prevalence of diseases for samples submitted to our diagnostic service (1 January 2020 – 28 October 2022).