Maryland Grows

Wildfire smoke

Persistent wildfire smoke is new for Maryland gardeners. Experts seem to agree that smoke and ash do not pose a health risk for garden produce. Smoke diffuses sunlight but will probably not significantly reduce the total amount of light for photosynthesis. We have not heard/seen any reports of gardeners picking up smoky flavors in harvested greens or other vegetables or fruits.

• Wash all produce prior to eating it raw or cooking with it
• Wear an N-95 quality mask when working outside on days when wildfire smoke worsens air quality
• Hose off plants if a noticeable soot layer develops from prolonged, intense smoke

Wildfire smoke has been shown to boost the levels of ozone and other air pollutants which can injure plants. Watermelon, squash, pumpkin, beans, and potato are especially vulnerable to high ozone levels (above 75 ppb).

Drought and damaging storms

Wildfire smoke interfered with weather patterns and likely contributed to cooler and drier weather across much of the state. 

Mid-May through June:

• Lower average temperatures
• 75% of state in moderate drought on July 3rd
• Slow start for warm-season crops

July:

• High heat and humidity
• Spotty rainfall
• Insect and disease issues increasing

Extreme weather is a hallmark of climate change. The mid-Atlantic region will continue to be warmer and wetter due to global warming but we will also experience periodic and deep drought. Drip irrigation is an efficient way to water containers and vegetable beds. It saves time and water and directs water to the root zone. Robert Cook, a UME Master Gardener in Baltimore City led a workshop in May on installing and using drip irrigation in the Master Gardener Learning Garden at the Maryland State Fairgrounds.

Speaking of extreme weather, parts of Anne Arundel Co. received 5+ inches of rain in late June from storms that included large hail. Here’s an example of hail damage to beans in the Master Gardener Demonstration Garden at the Extension Office. The plants will recover, but wow, were they surprised!

Vegetable problems we’ve been seeing

The causes of tomato wilting (healthy, green leaves and stems going limp) can be many: drought, excess water, stem boring insects, root injury, and diseases. Some gardeners have reported wilting, lower leaf yellowing, AND tan to brown discoloration of vascular tissue (photo below). These are major Fusarium wilt symptoms. Plants do not recover from fungal and bacterial wilt diseases. They should be removed and discarded with household trash. Heirloom cultivars are more susceptible than hybrid cultivars. Rotate tomato plants to a different location for at least 3—5 years and select cultivars with disease resistance, including resistance to the three races of Fusarium wilt (F_{1, 2, 3}). 

The container cherry tomato plants in the photo below are healthy and productive. Lower leaf yellowing and dieback occur naturally in garden tomato plants but in the second photo, it is more premature and dramatic, probably due to one or more stressors. Keep container tomatoes well-watered (next year, self-watering containers can help) and fertilize every 2-3 weeks. Unless growing very compact “patio” type cultivars, the minimum container size should be 5 gallons. 

Tomato plants are super-sensitive to 2, 4-D and other growth regulator herbicides. A very small amount can drift on air currents from a mile or more away can ruin one or more plants. New growth comes out twisted, distorted, and stunted. Plants almost never recover. Once you’ve mourned your loss, you can get a friend or neighbor to donate a tomato sucker as a replacement for a late tomato crop. This should work all the way up to early July in Western Maryland and up to the 3^rd week in July in other regions.

Many different cucumber and squash diseases (fungal, bacterial, and viral) overwinter in and around our gardens, are blown in from the south (usually) on storm fronts, or spread by insect feeding. It’s a rare garden that has not a single cucumber or squash disease. They can be difficult to distinguish based on symptoms but are managed much the same: clean up and dispose of all garden residues, plant disease-resistant cultivars, give plants the water, nutrients, light, and space they need to be healthy, and plant several times to hedge against losses and extend the growing season.

The photos below show the early and later stages of anthracnose, a common fungal disease. Notice how the symptoms change with the center portions of older lesions drying and dropping out. These diseases are progressive and fungicides available for home gardeners are generally ineffective once symptoms are observed.

You may have seen the type of Exobasidium fungal disease that causes galls on the leaves and flowers of azaleas and rhododendrons. It looks like we have a new type, Exobasidium leaf and fruit spot, that has moved up from Southern states and infects blueberry plants. This disease was confirmed by Karen Rane, Director of the University of Maryland Plant Diagnostic Lab, after an initial diagnosis by Sue Christensen, Extension Program Asst., Carroll Co. These photos show the distinct leaf and fruit symptoms. Please contact HGIC or your county/city Extension office if you see this disease.

Enjoy your garden and all of the problems that help us grow in humility and knowledge.

Resources

Wildfire smoke
Oregon State University
University of Delaware
NY State Government
Scientific American- ozone and wildfires

Climate-resilient gardening
University of Maryland Extension website and Maryland Grows blog
Climate Webinars, Sara Via, Ph.D.
Maryland Department of Agriculture – Practice Climate-Smart Gardening

Plant problems
Air Pollution Effects on Vegetables
Key to Common Problems of Cucumber
Key to Common Problems of Tomato
Key to Common Problems of Squash
Cornell University- Disease-Resistant Varieties

By Jon Traunfeld, Extension Specialist, University of Maryland Extension, Home & Garden Information Center. Read more posts by Jon.