University of Missouri Plant Diagnostic Clinic 2021 Semiannual Report for Horticultural Crops

Published: August 20, 2021

MU Plant Diagnostic Clinic (MU-PDC) reopened on February 1^st, 2021. As of August 13th, 2021, we have received 214 samples including physical samples, walk-in samples and digital samples. Among all the samples, plant disease diagnosis accounted for the majority of the total samples while only three samples are for insect identification services and no sample for weed identification (Figure 1). Out of 211 disease diagnosis samples, 15 samples were suspected to have herbicide injury and 12 samples were confirmed with winter injury, indicating that the off-target chemical damage as well as cold injury played important roles in affecting plant health this year. The samples submitted to the clinic were also categorized based on the crop types (Figure 2). Ornamentals were the largest sample category with 71, followed by field crops (47), vegetables (38) and turf (19).

Figure 1 Number of samples by type of disease

Figure 2 Number of samples submitted for disease diagnosis by sample category

Figure 3 Number of ornamental samples submitted for disease diagnosis by sample category

The woody ornamentals are the primary source of samples submitted to the lab and this category includes evergreen plants such as juniper, cypress and spruce pine and deciduous plants such as maple, oak and tulip trees (Figure 3). As far as vegetable, tomato takes up the majority of the samples submitted to the clinic.

The weather of the first half of the year was not very kind for many horticultural plants but very favorable for several fungal diseases. The humid condition early in this season was very conducive for many types of plant pathogens, especially fungal and bacterial pathogens. Based on the weather reports in the past months, we had a very cold month in February, then heavy rainfall followed by a very short period of hot and dry weather in March. After that, we had half of a month with heavy rainfall again.

Under this cool and wet condition, many fungal pathogens such as Anthracnose or Cercospora become very aggressive for both woody ornamental, perennials as well as vegetables. Regarding the tree diseases, most of them are related to winter injury. Fungal diseases such as Phomopsis and Dothistroma needle blight became more prevalent on the susceptible trees under environmental stress. Several maple, oak and sycamore trees samples were confirmed with Anthracnose, Cercospora leaf spot and target spot diseases. In addition to foliar and needle diseases, there were four cases of oak wilt disease confirmed by my lab and we may see more oak tree samples suspected with this disease because July to October is the time that the symptoms become visible. As far as home gardeners and commercial growers of vegetables, chemical damage, root and crown rot diseases and foliar diseases are the three major health issues affecting the yield and quality. Disease management strategies of most of these diseases should be focused on sanitation and the use of resistant varieties.

For appropriate diagnosis, the MU Plant Diagnostic Clinic can help you confirm if your plant has this disease. We encourage you to visit our website (https://extension.missouri.edu/programs/plant-diagnostic-clinic) and review submission guidelines before submitting your sample. If possible, you may take photos and send them to plantclinic@missouri.edu.

We uploaded a webinar about sample submission guidelines on YouTube to help you submit your sample step by step.
Please click here: https://www.youtube.com/watch?v=4dUcYKKFwaI

For sample submission and fee payment, you can either:

1) Visit our new online submission system at https://extension.missouri.edu/services/plant-disease-sample. Fill out the submission form online using your computer or mobile device and make payment online securely with a credit card.

2) Download the submission form at https://extension.missouri.edu/programs/plant-diagnostic-clinic/sample-submission. Fill it out and send to us together with your sample and payment. Check or money order. No cash please.

Contact Information:

University of Missouri-Plant Diagnostic Clinic
28 Mumford Hall
Columbia, MO 65211
Phone: 573-882-3019
Email: plantclinic@missouri.edu