According to our experts at the U of M Arboretum, frequent rains this spring and early summer have created favorable conditions for hollyhock rust. Hollyhock rust is caused by the fungal pathogen Puccinia malvacearum, which infects hollyhocks and related weeds like roundleaf mallow (Malva neglecta). Early symptoms of hollyhock rust are easily missed.

Small waxy yellow bumps form on the lower surface of the lower leaves of the plant. With age, these pustules turn reddish brown and a bright orange spot develops on the upper leaf surface. In wet years, spores from these early infections easily spread to infect leaves, stems, petioles and even flower bracts. Heavily infected leaves turn yellow and may wither and curl.

This significantly reduces the plant’s ability to do photosynthesis. The hollyhock rust fungi can survive from one season to the next in infected live crowns, as spores in infected plant debris, or on seed from infected plants. Unfortunately, it is too late to prevent hollyhock rust this season. Keep plants as dry as possible by avoiding sprinkler irrigation and pulling weeds to improve air circulation around the plants.

This will help to reduce spread of existing infections. Gardeners with infected plants should cut off the plant at ground level after flowering is complete. Infected plant material should be removed from the garden and buried, placed in a compost pile that heats up or taken to a municipal compost facility. Next year, mulch around the base of the plant to reduce the spread of spores from plant debris. Scout plants in early spring.

Look for yellow waxy pustules on the lower leaf surface. Infected leaves should be removed and buried or composted.

This year’s frequent rains have created ideal conditions for many fungal and bacterial diseases in the vegetable garden. These pathogens need moisture to reproduce, spread and start new infections. Although gardeners can’t change the weather, a few things can be done help plants dry out after rain or dew and to reduce the spread of disease: Space plants to allow for air movement around the plants and through the foliage. Dense planting results in fruit and foliage that stay wet longer; a favorable condition for many pathogens; pull weeds. Weeds crowd the vegetable plant, steal nutrients and reduce air movement in the garden; Completely mulch the soil with landscape fabric, plastic mulch, straw or wood chips.

Many pathogens survive in plant debris and soil. Rain and irrigation splash water, soil and pathogens onto the lower leaves of the plant. Mulch provides a barrier that reduces splash dispersal of the pathogen from soil to plant. In addition, mulch keeps moisture in the soil and reduces humidity in the plant canopy; stake vining plants like tomatoes, cucumbers and runner beans.

This will improve air movement around the plant and facilitate drying of the leaves and fruit; Do not work in plants when leaves and fruit are wet. Fungal and bacterial pathogens reproduce under wet conditions and can easily be spread on a gardener’s hands or tools at this time. Wait until plants have dried completely before working in the garden; pinch off heavily infected leaves and fruit and remove them from the garden. Many leaf spot and fruit rot diseases produce new fungal spores or bacteria in every leaf spot.

These pathogens are easily spread through the plant to new leaves and developing fruit. Infected plant material can be buried, placed in compost that heats up or taken to a municipal compost facility.

Remember many plants tolerate some leaf infection and still produce a good crop. Use the steps above to reduce the spread of disease and minimize its impact on your final harvest.