DRY WEATHER STRESSES TREES AND LAWNS, FRUITS AND VEGETABLES (Not to mention field crops)

 July 26, 2012

While what happens in lawns and gardens during hot, dry weather isn’t perhaps as critical to the economy of most of us as is what happens in the fields around us, it is still shocking and worrisome to see leaves falling off your trees 2 or 3 months ahead of schedule. The current situation is widespread across the region and people’s livelihoods are at stake. If you have a lawn care business, that has suffered, as have the golf courses. Orchards, corn and soybean growers and more are adversely affected as well. I am merely concerned for my trees and hostas, which survival is not important to my business. Losing them, however, would affect me economically as I would have to replace them at major cost. Irrigating is in itself an
economic factor. If the drought worsens, communities could see reductions in water availability. I have 2 well-established trees that have browned and are losing leaves and my river birch, planted 5 years ago, has yellow falling leaves. Probably your trees and mine will survive, unless they were in poor health to begin with or have only been planted within the past three to five years. Trees planted more recently than that need to be watered deeply every week to 10 days, in a normal year. The newly planted trees don’t have the root system to cope in abnormally dry years and need to be watered to survive. Once you start watering you cannot stop until 1-inch rains become common. Only you can decide whether to lend a hand or let Mother Nature determine the outcome.

Some trees, like the river birch, cope by shedding their leaves to conserve moisture while others may just appear to be dying. Indeed, they may be dying if your tree is unhealthy even though it appeared to be fine. The added stress of drought will speed up the decline of these trees according to Jesse Randall, Iowa State University Extension and Outreach forester. It is always difficult to lose a tree, especially if it is a good shade tree, so precautions can help eliminate or reduce losses. Watering in early morning or late evening is best, giving the tree a good soaking.

I attended the drought webinar at the extension office last week, which attempted to answer the questions of whether or not to intervene. In a nutshell, it is best to protect your investment in trees if they are under the age of 7 years. For mature trees, forget it. How much water, you say, and how often? Normally, a watering one to three times a week for the first few months when they are first planted is sufficient. The area under the canopy should be slow watered daily on the surface in extreme conditions, such as we are experiencing,
with 2-4 gallons per inch of trunk caliper. This can be scaled back according to time of year and weather. The hotter and windier it is the quicker the plant loses water. Trees with insufficient water will experience increased insect and disease problems and even root death. Mulching helps conserve moisture as well as enhancing your landscape and keeping the weeds at a minimum. Mulch around your trees also keeps lawnmowers and other potentially damaging equipment away from the trunk.

In general, whether you are watering your lawn, vegetable garden, flower beds or trees, a schedule that allows 1-1½ inches of water per week to each area is best carried out in the early morning hours from 6-9 a.m. This allows for most of the water to soak in deeply with the least amount of evaporation. Midday watering is less efficient, especially when using a sprinkler, due to increased evaporation and stronger winds that can carry the water away from where you want it, causing uneven watering and waste. Watering in the evening can increase disease problems. When watering the lawn, if you choose to do so, a single application of 1-1½ inches of water allows the roots to penetrate more deeply into the soil than does frequent shallow watering. Shallow rooted turfgrass is more susceptible to pests and is also less drought tolerant. If you are
sprinkling, place 2 or 3 containers or rain gauges within the spray pattern to judge the amount of water you are applying. According to Dave Minner, a webinar presenter on turfgrass, there is no one good answer as to whether or not to water. Most lawns are just dormant from the drought, but could be dying in some cases. Dry, brown grass with roots in thatch may die, as well as roots in sand. For dormant lawns during drought, Minner recommends watering with 1” of water every 3 weeks and if you are mowing, cut grass no shorter than 3-1/2” in height. One other thing to consider is planting more drought-resistant types of grass, such as turf type tall fescue, especially if your lawn dies and you need to replant.

Minner’s bottom line, “Pray for rain, but prepare for drought.” Ajay Nair spoke on fruits and vegetables, saying first “There are major vegetable issues. First there was the April frost, Japanese beetles in some areas and now the excessive heat and drought.”

The heat and lack of rain affects crop establishment, plant growth and development. Temperatures over 95 degrees significantly reduce pollen count and viability. Poor pollination equals poor quality crops. At those temperatures, or with water stress, vegetables such as beans, tomatoes, peppers, and peas will drop their flowers. One product on the market is a cooling spray called Surround, which reduces canopy temperatures, though it may need to be re-applied every 7-14 days.

Taking a soil sample at the beginning of the growing season to determine if extra calcium fertilizer needs to be applied is a good idea. A lack of calcium, not enough water to move the calcium even if present, too much nitrogen, inadequate moisture or high soluble salt concentrations in the soil near the roots can result in blossom end rot. These issues can be determined with a soil sample, and steps taken for prevention.
Managing fruits in drought is a bit more complicated and watering needs depend on several factors including soil texture, soil depth, rooting depth of the crop, crop development and factors affecting the need for water (heat, light, humidity and wind) Soil moisture content should be at 50-80% for optimum growth. Below 50% plants show stress.

For example, strawberries have a rooting depth of 1 inch and should be watered to a depth of 6 inches; raspberries, blackberries, gooseberries and aronia berries have a root depth of 2 inches and need water at 12-15 inches. Tree fruits and grapes have 3-foot roots and need water at 24-30 inches. There is not “one size fits all” answer to the irrigation issue for fruits, and is a lengthy subject deserving its own column.

For fruits and vegetables as well as flowerbeds, a soaker hose or drip irrigation system is more efficient and causes fewer disease problems than sprinklers. Also, keeping weeds at bay is as important as water management, as the weeds compete for both water and nutrients. Yes, hot and dry conditions are troubling on many fronts, but for those of us who like to grow things it is especially difficult when the gardens start to go downhill. However, gardeners are optimistic, as are farmers, and surely next year will be better.

To get an answer to a specific question there are specialists available at hortline@iastate.edu or you may call 515-294-3108. The Yard and Garden FAQs website at http://expert.hort.iastate.edu/ is a good place for answers to tree and other yard and garden questions.

Julie Johnston, Master Gardener intern