New Vegetable Gardeners Face Old Problems

“What’s that bug doing on my bean plants”? “Should I be worried by these droopy leaves”? “Help – the lower leaves on my container tomato plants are turning yellow. What should I do?”

HGIC is receiving many questions from first-time vegetable gardeners this year through our Ask Extension service. It’s great to see more people growing some of their own food! We are trying to address specific concerns and help people learn how to prevent problems and garden sustainably and lovingly on Planet Earth. Our food gardens can be peaceful and restorative spaces and exciting laboratories where problems can be learning experiences.

Here are some of the major concerns of new vegetable gardeners:

Plants just don’t get big and healthy

The first step in IPM (integrated pest management) is to know and meet the needs of your plants. Healthy, resilient plants are better able to withstand pests, diseases, and challenging weather. When plants look weak, under-sized, and stressed we need to ask some basic questions: Is it the right plant for our climate? Does it get enough sunlight, and does it have enough room to grow? Is the container too small? Was it planted at the right time? Is the plant getting enough water and nutrients?

Cauliflower with spotty leaves
Cauliflower is a challenging spring crop. It’s early July and these plants are too
small and too late to produce heads. Close spacing, inadequate nutrients, and a disease
(black rot) are possible causes.

No fruits from summer squash and cucumber plants

Many gardeners are frustrated by plants that aren’t producing many (or any) fruits. This family of plants requires cross-pollination. Pollinating insects must move pollen from male to female flowers multiple times before a full-size fruit will form. Most of the first flowers are male flowers and when female flowers do appear (they can be identified by the small, undeveloped fruit below the flower) they may drop off. Small fruits may also dry up and drop off. This is caused by incomplete flower pollination or fertilization of the tiny undeveloped seeds (ovules), caused by low pollinator activity or heat stress. If the plants are healthy you will start to see more fruits as the season progresses. In the meantime, you can try hand-pollinating individual female flowers using a small, soft paintbrush or the male flower itself. There are many online videos to show you the way.

Male squash flowers
Male squash flowers on long slender stems (pedicels) may outnumber female flowers 10:1.

Spots, marks, blotches on leaves

Plant leaves do not need to be perfect to be healthy. Some leaf spots are indeed symptoms of a disease, insect or mite pest, and some of these can injure and kill plants. However, many leaf imperfections are not a cause for alarm. They may be caused by minor insect feeding, environmental conditions, and even misuse of fertilizers and pesticides.

Plant burn on leaves
No disease here. This is phytotoxicity (plant burn) from spraying a home-made liquid detergent solution on bean plants.

Wilting leaves and stems

Plant leaves and stems that begin to go limp are a serious concern. A lack of moisture is the most common cause, especially for container vegetables or gardens planted in sandy soil. Root damage from cultivation, insect feeding, diseases, and waterlogged soil can also cause wilting symptoms. It’s important to quickly figure out why a plant is wilting.

Cucumber leaves wilting
Cucumber leaves wilting from bacterial wilt disease spread by cucumber beetles. Plants recover at night, but the wilting symptom progresses and kills them.

Distinguishing major and minor insect pests

Hundreds of different insect species will visit your garden each year. Some are beneficial to gardeners, many are innocuous, a few are minor pests, and a very small number are serious pests. They are all fascinating and interesting to observe! Close monitoring of plants, including leaf undersides, will help you detect and manage the serious insect and mite pests:

These are examples of three relatively minor pests in vegetable gardens:

An Oriental beetle adult visiting an okra leaf
An Oriental beetle adult visiting an okra leaf
adult golden tortoise beetle
An adult golden tortoise beetle with fecal shield to ward off predators. This minor feeding injury on tomato, sweet potato, and other plants can be ignored.
Pigweed flea beetles (that resemble cucumber beetles) on leafy amaranth.
Pigweed flea beetles (that resemble cucumber beetles) on leafy amaranth. Plants continue to grow and remain healthy.

When to cut your losses?

Every growing season you will probably have some crops that fail for a variety of reasons. Your garden will be more productive if you learn when it makes sense to pull out ailing plants and re-plant the area. Of course, figuring out what caused the plants to fail is the key to preventing the same problem next year.

Cucumber leaf with holes
This level of cucumber beetle (major pest) feeding can significantly weaken plants. If all the leaves look like this or worse and fruit production is reduced, it’s time to yank out and compost plants.

Tips for dealing with plant diseases

Many bacterial, fungal, and viral diseases attack vegetable crops in Maryland home gardens. Most of them can be managed without significant yield loss and in very few cases is spraying a fungicide recommended.

Foliar diseases can vary in severity from season to season according to rainfall and temperature. Regular plant inspection, especially on lower and inner leaves, will alert you to problems. Foliar diseases are progressive- they begin as small spots on a few leaves. Lesions grow and coalesce and may cause leaves to yellow and die. Identify problems early on to determine the cause of the problem.

  1. Select disease-resistant varieties, particularly for those diseases that appear in your garden each year.
  2. Purchase certified, disease-free potato tubers, garlic bulbs, and asparagus and rhubarb crowns.
  3. Avoid planting on wet, poorly drained sites. Plant in raised beds if drainage is not very good.
  4. Add organic matter to your soil each year.
  5. Grow healthy plants by providing adequate light, water, and nutrients. Give each plant adequate space to ensure good air circulation.
  6. Keep bare ground covered with an organic mulch.
  7. Avoid watering foliage in the evening. It is best to use soaker hoses and drip irrigation, or water around the plant base where it can quickly reach the root zone.
  8. Avoid handling wet foliage.
  9. Harvest your vegetables before they become over-ripe.
  10. Cut off and discard leaves and pull up and discard entire plants that are badly infected by disease.
  11. Clear your garden at the end of the season of all plant debris. This should be composted or tilled into the soil. Plant parts infected with especially damaging diseases, like late blight of tomato and potato, southern blight, and white rot (garlic and onions), should be bagged and put out with your trash.
  12. Keep weeds to a minimum and control those insect pests like thrips, aphids, flea beetles, and cucumber beetles that are most likely to spread diseases.
  13. When disease symptoms are observed it is often too late to apply a fungicide, although fungicide treatments can help to protect new or un-infected foliage. Fixed copper, sulfur, and horticultural oil are some organic fungicides used by home gardeners. Always, carefully read and follow all pesticide label information and test the spray on a small part of the crop to check for signs of leaf injury (phytotoxicity). Don’t spray on very hot and humid days.

Keep notes this year on plant issues to help you avoid them or manage them better next year. Keep planting and growing!

By Jon Traunfeld, Extension Specialist. Read more by Jon.

Boxwood Blight in Maryland

Until last summer most people in Maryland weren’t aware of the new fungal disease infecting boxwood called boxwood blight. In 2011 professionals in the green (landscape and greenhouse) industry were informed of the disease but the outbreaks were scattered and insignificant. However, the rainy 2018 season greatly increased the spread of the disease. It has now become more noticeable in Maryland landscapes. In addition, on a few occasions, it has been observed on Japanese spurge (Pachysandra terminalis) in Connecticut and on sweetbox (Sarcococca sp.) in Maryland and Virginia. Essentially, boxwood blight occurs up and down the east coast.

Boxwood blight will infect all boxwoods grown in landscapes. However, some cultivars, especially English and American, are more susceptible than others. See the following photos for symptoms of boxwood blight.

boxwood blight leaf lesions
Dark leaf spots are a symptom of boxwood blight. Photo: Dave Clement
boxwood blight stem lesions
Narrow black lesions (cankers) on green stems are a key symptom of boxwood blight. Photo: Dave Clement
boxwood blight lesions on dead stems
Black lesions on stems of boxwood. Photo: Dave Clement

This slideshow requires JavaScript.

So the question is what to do if your shrubs are diagnosed with boxwood blight? The best information for homeowner action is located on the Virginia Boxwood Blight Task Force website: Best Management Practices for Boxwood Blight.

Here is a quick summary of what to do in the landscape:

  • A strong suggestion is to avoid planting any new boxwood plants in your existing landscape or bringing in boxwood greenery, including holiday boxwood wreaths.
  • If planting, inspect your plants carefully and ask if the plants have been raised in a certified “cleanliness program.”
  • Observe and watch any newly planted boxwoods carefully for disease symptoms.
  • Send photos of suspicious symptoms to the Home & Garden Information Center’s Ask Extension service.
  • If disease symptoms are diagnosed, immediately bag and remove infected plants along with fallen leaves. Mulch the area to bury remaining debris. Do not compost infected boxwood material. Launder all clothing, gloves, and shoes, and sanitize gardening tools.  Removal will not guarantee eradication of the boxwood blight pathogen since it can survive in resting structures in the soil for many years.
  • Fungicide sprays have shown some disease suppression in limited situations. However, these treatments do not eradicate boxwood blight and need repeated applications throughout the growing season.
  • Consider replacement of boxwoods with non-susceptible plants such as hollies and conifers.

By Dr. Dave Clement, Principal Agent, University of Maryland Extension, Home & Garden Information Center. 

Why is My Tree (Or Shrub or Flower) Dying? Abiotic Problems Could be the Cause

freeze damage on hydrangea
Hydrangea leaves damaged by a late spring freeze. Photo: D. Ricigliano

Professionals in the landscape and greenhouse industry, trained horticulturists, and Master Gardeners often use the term “abiotic disorder” when diagnosing a plant problem. To the layman, this can be very confusing. To add to the confusion, signs and symptoms you see on your plants can look very similar to the damage caused by insects and diseases.

Surprisingly enough, the vast majority of plant problems are not caused by insect pests or diseases. Typically, the first thought that comes to mind when a plant is looking “ill” is that some insect or fungus has attacked it without much thought that it could be something else.

Continue reading