Sample Diagnosis

In the first half of 2024, the MU Plant Diagnostic Clinic has received 297 physical samples and 139 digital samples (Figure 1). The 297 physical samples include services of plant disease diagnosis (283), insect identification (8), and plant identification (6). Like previous years, the lab received the most submissions in the summer months (Figure 2 and 3).

Figure 1 Number of samples by service type.

Figure 2 Comparison of physical sample number by months in 2021-2024.

Figure 3 Comparison of digital sample number by months in 2022-2024.

Sample Submission

287 in-state physical samples were received from 44 counties (Figure 4). 175 samples were submitted by commercial clients. Submission received directly from educators and homeowners accounted for 41% of the total physical samples processed in 2024.

Figure 4 Counties submitting plant disease samples to the clinic.

Sample Category

Samples submitted to the clinic were categorized into different crop types such as field crops, turf, ornamentals, vegetables, and fruits. Field Crops are the largest sample category with 110 samples, followed by Fruits (98), Ornamentals (68) and vegetables (16) (Figure 5).

Figure 5 Distribution of samples submitted for disease diagnosis by sample type.

Figure 6 Types of Ornamental Plants submitted to the clinic in 2024.

Summary of Fruit and Vegetable Crop Diagnosis

Among the diagnosed fruit and vegetable samples, we received 39 Elderberry samples followed by 15 Tomato and 12 grape (Figure 7). A certain amount of vegetable samples submitted by home gardeners and commercial growers were shown to be affected by chemical damage (suspected products containing Dicamba and 2,4-D) in the beginning of the season. Some Oomycete diseases such as Phytophthora or Pythium crown and root rot were found early in the season. Overall, root and crown rot diseases, vascular diseases and foliar diseases are three major plant health issues affecting the yield and quality through the season. Disease management strategies for most of these diseases should be focused on sanitation and the use of resistant varieties.

Figure 7 Summary of the types of fruit and vegetable samples submitted to the clinic.

Most Missouri counties experienced drought for several months in 2022 and 2023. By spring of 2024, Missouri had experienced drought throughout the winter, and then there were several heavy rains when planting season began. Now, we have seen minimal rainfall since the beginning of the summer. These conditions have led to environmental stress being a root cause for most of the problems seen in the horticultural plant samples submitted to the MU-PDC. Environmental stress related problems for woody ornamental plants were prevalent as the clinic observed several submissions of diseased samples of deciduous and evergreen trees from multiple counties (Figure 6). Most of these samples were diagnosed as abiotic diseases such as winter injury or drought stress. Oak Wilt was observed from one red oak sample earlier this year, which means homeowners should be cautious when moving firewood or pruning trees during the spring and summer. Among evergreen trees, the environmental stress of heat and drought throughout the start of the year could lead to needle yellowing and stem dieback. Symptoms may vary among different families of trees and may take one or two following seasons to appear. Once these symptoms appear in woody plants, the disease or stress is generally beyond treatment. Clients may consider keeping good irrigation for their trees even in the winter, performing a soil test early in the spring for recommendations regarding soil fertilization, and pruning dead branches when the trees are still dormant. Consult an arborist if there are any questions related to tree care and be sure to submit suspected disease samples to the MU PDC when symptoms appear.

Other ornamentals such as shrubs, annuals and perennials did not show many diseases in the first half of 2024 except boxwood, which continued to show symptoms of stress from both abiotic and biotic factors. Oomycete and fungal soilborne diseases are prevalent in vegetables and similar incidence also occurred in vegetables, fruit trees and turfgrass. Fungal diseases that are normally prevalent in dry weather include Fusarium root rot and Rhizoctonia crown and root rot, were detected from a few vegetable samples.

The drought conditions, along with a short burst of sudden rain during planting has stunted root growth in some cases. Issues of herbicide damage were common this year, but less than the past two years. With limited rainfall and lack of soil moisture, the normal breakdown of herbicides in the soil can be delayed. In heavy rainfall events, herbicide previously present within the soil can be taken up by the plant, leading to symptoms of exposure. In the case of drought, herbicide residues persist for longer periods, leading to increased damage to crops and vegetation. The lack of consistent moisture has reduced plant vigor, making them more susceptible to herbicide, environmental stress and disease, hindering their ability to recover in adverse conditions.

It is always hard to predict the performance of the plants and prevalence of plant diseases right after a year with severe drought. Depending on the weather of this winter and spring of 2024, cold injury and excessive rainfall would worsen the situation of most ornamentals and vegetables, while continuous drought would result in more environmental stress on all plants.

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.

Contact Information:

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