Pests of Stressed Plants

The following are some common pests of stressed plants. We are seeing drought stress in many parts of the state now.

Aphids and whiteflies are apparently drawnt o plants with yellowing foliage. Plantsunder stress often lose some of their chlorophyll and become yellowish in color. Yellow sticky cards are often hung in greenhouses to monitor for some of these pests.

Some species of caterpillars (not gypsy moth) are “samplers” when they feed. These caterpillars will sample individual leaves to determine if they contain plant defensive chemicals such as tannins or alkaloid toxins. If these toxins are contained within the leaves, the caterpillar may find it distasteful and move on to sample other leaves. A weakened plant unders tress may not have enough energy to produce these defensive chemicals and therefore, be more attractive for these caterpillars.

The greatest concern with stressed plants in the landscape is from borer infestations. The best examples of borer-prone plants are when drought conditions and high temperatures stress non-native plants. Pine bark beetles, bronze birch borers, and the two-lined chestnut borers are all encouraged when stressed tress are forced to “shutdown”their vascular systems (xylem& phloem tissues). When trees have low sap pressure, the borers can easily penetrate and cut through vascular tissue. Furthermore, trees with compromised vascular systems cannot readily transport defensive chemicals to areas invaded by borers.

Adapted from a presentation delivered by Dr. David Shetlar (The Ohio State University Extension)@ the RCE IPM Symposium, Nov. 1995

Safety - More on Heat Safety

I came across another good article on heat safety for horticultural workers from Iowa State University and thought I would share it with you.

As temperatures rise, so can problems related to heat. As gardeners and horticultural workers, we need to be aware of how serious heat related illnesses can be and how to avoid them. If the body does not rid itself of excess heat fast enough, it cooks the brain and other vital organs. Heat stroke is often fatal, and those who survive may have permanent damage to their vital organs.
The human body loses heat through the skin by radiation and evaporation (vaporization of sweat). When the temperature is 70 or less, the body releases its heat by radiation. As the air temperature approaches body temperature, less heat is lost through radiation. In fact,people working on hot summer days actually gain heat through radiation from the sun. This leaves evaporation as the only way to effectively control body temperature. Since the body is made up of about 50% water, a working adult can produce 2 quarts of sweat per hour for short periods and up to 15 quarts per day. The body can only absorb water at the rate of 1.5 quarts per hour. This is less than what can be lost through sweat and, as a result, dehydration occurs. If liquids are consumed only when you are thirsty, you are dehydrated already. Thirst is not a good indicator for when to drink water. While working in hot weather, drink 8 ounces of water every 20 minutes. Generally, 16 ounces is the most a person can comfortably drink at once. Unfortunately, the human body cannot "catch up" by drinking extra water later in the day because only about 1 quart of water per hour can pass out of the stomach. Therefore, people should begin drinking water before working outdoors.

Cool water (50 F) is easier for the stomach to absorb than warm water, and a little flavoring may make the water taste better. The best fluids are those that leave the stomach fast, contain little sodium, and less than 8% sugar (water). Avoid coffee and tea because they contain caffeine which increases water loss through urination. Alcoholic beverages also dehydrate by increasing urination. Pop and fruit juices contain more sugar than needed so they aren't absorbed as easily or quickly as water or commercial sports drinks. Commercial sports drinks contain about 5 to 8 percent sugar. These can be useful if you are participating in vigorous physical activity for longer than 1 to 4 hours.

Can a person drink too much water? Yes, drinking more that 1 quart of water an hour can cause water intoxication which can be signaled by frequent urination and behavior changes such as irrationality, combativeness, coma, seizures, etc.

Sweat only cools the body if it evaporates. In dry air, we won't notice sweat evaporating. At about 70% humidity, sweating is ineffective in cooling the body because it just drips off the skin. Because humidity can significantly reduce evaporative cooling, a highly humid but mildly warm day can be more stressful than a hot, dry one. The higher the humidity, the lower the temperature at which heat risk begins, especially for those who are working vigorously. Thus there is truth to the saying that it's not the heat but the humidity that will kill you.

Everyone is susceptible to heat illness if environmental conditions are favorable. People who are obese, chronically ill, elderly, outdoor laborers, infants and small children can be of higher risk for heat illness. Certain medications can also predispose individuals to heatstroke or interfere with thermoregulation. Several heat illnesses exist with varying degrees of severity. Heat cramps, heat exhaustion, and heatstroke are on the more serous side, while heat syncope, heat edema, and prickly heat are less serious.

Heat cramps are painful muscular spasms that occur suddenly usually involving muscles in the back of the leg or the abdomen. They tend to occur immediately after exertion. To remedy the situation, sit or lie in a shaded, cool location. Drink cool, lightly salted water (0.25 tsp inwater) or a diluted sports drink. Also, stretch affected muscles.

Heat exhaustion or severe dehydration is characterized by heavy perspiration with normal or slightly above-normal body temperatures. Symptoms include severe thirst, fatigue, headache, nausea, vomiting and diarrhea. Affected individuals often mistakenly believe they have the flu.Uncontrolled this can evolve into heat stroke. To relieve the symptoms, follow the same recommendations given for heat cramps. If symptoms persist longer than 20 minutes, apply wet towels and call for an ambulance. Do not give salt tablets. Raise the victim's legs 8 to 12 inches keeping legs straight. Remove excess clothing and sponge with cool water and fan.

Heat stroke is classified in two ways: classic and exertional. Classic heat stroke may take days to develop and is prevalent during summer heat waves. It typically affects the elderly, chronically ill, alcoholic or obese persons. Exertional heat stroke is more common in athletes, laborers and military personnel who sweat profusely. Because uncontrolled heat exhaustion can evolve into heat stroke, you should know how to tell the difference between them. If the victim feels extremely hot when touched, suspect heat stroke. Another symptom characteristic of heat stroke is that the victim's mental status (behavior) changes drastically ranging from being slightly confused and disoriented to falling into a coma. In between these conditions, victims usually become irrational, agitated or even aggressive and may have seizures. A third way to tell is through rectal temperature, which may not be the most practical method when time is of utmost importance. If you suspect heat stroke, seek emergency help immediately.
Heat syncope occurs when a person becomes dizzy or faints after exposure to high temperatures. Victims should lie down in a cool place when it occurs. Victims who are not nauseated can drink water.

Heat edema causes ankles and feet to swell from heat exposure. It is more common in women unacclimated to a hot climate. Wearing support stockings and elevating the legs often helps reduce swelling.

Prickly heat, also known as heat rash, is an itchy rash that develops on the skin that is wet from sweating. Dry and cool the skin to relieve the condition.

Prevention and protective measures are the best way to avoid problems. Acclimating to the heat is an important preventive measure. Year-round exercise can help outdoor workers prepare for hot weather. Exercising for 60 to 90 minutes in the heat each day for 1 to 2 weeks will help the body decrease salt content in the sweat and increase the sweating rate. When new workers are exposed to hot weather, team them with veterans who know how much water to drink to avoid dehydration. A good rule of thumb for fluid replacement is to drink 1 cup of water every 20 minutes while working. Dress in light colors to reflect the heat. Wear porous and loose fitting clothing that allows evaporative heat loss and air to circulate to your body. Rest frequently, preferably in the shade. Wipe cool water on exposed areas in the skin. Dip clothing periodically in water to help cool the skin.

Sometimes the only way to stop possible heat illness and prevent irreparable damage is to cool the victim as quickly as possible. Ice baths cool a victim quickly but require large amount of ice to be effective. Cool water baths can be successful if you stir the water to prevent a warm layer from forming around the body. This is the most effective method in highly humid conditions. Spraying the victim with water combined with fanning is another effective method, though not as effective in high humidity. Ice bags wrapped in wet towels and placed against the large veins in the groin, armpits and sides of the neck also cool the body, though not nearly as quickly as immersion. Some cautions need to be remembered when employing any cooling method. Do not delay the onset of cooling while waiting for an ambulance. Doing so increases the risk of tissue damage and prolonged hospitalization. Stop cooling when the victim's mental status improves to avoid hypothermia. Do not use rubbing alcohol to cool the skin. It can be absorbed into the blood, causing alcohol poisoning. Do not use aspirin or acetaminophen. They are not effective in reducing body temperature because the brain's control-center temperature is not elevated as it is with fever caused by diseases.

Summer is upon us, take the necessary precautions to make sure it as safe as possible.

This article originally appeared in the June 20, 1997 issue, pp. 95-97 of the Horticulture and Home Pest News from Iowa State University. Article by Sherry Rindels, Department of Horticulture.

Safety - Drinking Water Program for Workers During Hot Weather

Provision of adequate drinking water and making sure employees drink enough is extremely important during hot weather. The following is information on this subject.

Drinking water is most important in maintaining workers’ health and performance in the heat. A leading cause of heat illness is dehydration, which reduces the body’s ability to disperse heat through sweating. The water needed to replace lost body fluids varies among individuals, and is affected by temperature, humidity, and type of work. Daily water needs for moderate summer work in temperate regions ranges from 6 to 10 quarts. On hot days, a worker can lose 3 gallons of perspiration. At low humidities, you can sweat heavily and still have dry skin. In extreme heat, you can sweat up to 2 quarts per hour, but this rate can not be tolerated for long!

Drink enough water to maintain body weight. Sharp weight losses indicate inadequate water. Other indications are dark yellow urine, and passing less urine than usual. "Weighing in" each morning is a way to monitor weight. Remind workers often to drink water, even when busy.

Thirst does not measure water needs. Workers drinking water only to satisfy thirst drink about two-thirds of that needed. This can mean a weight loss of 2 to 4 pounds on hot days. Chronic dehydration can develop gradually over several days, without thirst. It can lead to such health problems as kidney stones and urinary infections.

Generally, workers in the heat should drink at least a cup of water each 30 minutes, and greater amounts in extreme conditions, even if they are not thirsty. It is easier to drink smaller amounts of water frequently than larger amounts less often. Drinking several cups of water before work gives you a head start. Experienced, “heat-adjusted” supervisors and workers who have not previously followed a strict "by the clock" water-drinking schedule may be surprised at the reduction of heat strain.

Workers should not deliberately limit the water they drink to keep from stopping to urinate. In hot conditions, drinking lots of water does not cause an increase in urine, unless you’ve consumed excessive caffeine.

Generally, 2-3 gallons per worker per hot day is enough. Water temperature should be 50 to 60 degrees F. Most people tend not to drink warm or very cold water in quantity as willingly as cool water.

Soft drinks are not recommended as beverages to replace body fluid. The gas makes them hard to drink in quantity. Dilute ice tea or lemonade are alternatives if sugar content is low. Unfortunately, drinks that “cut” thirst discourage sufficient fluid replacement.

Balanced diets usually contain enough salt, even in hot weather. Heavy salt diets may interfere with heat adjustment, causing illness.

Alcohol increases the risk of heat illness and injuries. Urge workers not to drink alcohol during hot weather before work, and until the end of the evening meal after work, to give their body a chance to replace fluids. Employees who are under the influence of alcohol on the job compromise the employer's interests, endanger their health and safety and the health and safety of others, and can cause a loss of efficiency, productivity, or a disruptive working environment.

Information from "A GUIDE TO AGRICULTURAL HEAT STRESS" from the AGRICULTURAL PERSONNEL MANAGEMENT PROGRAM NEWSLETTER, University of California Cooperative Extension, Fresno, Kings, Madera, and Tulare Counties.

Safety - Heat Stress

With the high temperatures in the past few days and more expected, horticultural employers should become familiar with signs of heat related disorders and take precautions to protect employees. The following is information on the the types of heat related disorders and their symptoms.

High temperatures and humidity stress the body's ability to cool itself, and heat illness becomes a special concern during hot weather. There are three major forms of heat illnesses: heat cramps, heat exhaustion, and heat stroke, with heat stroke being a life threatening condition.

Heat Cramps

Heat cramps are muscle spasms which usually affect the arms, legs, or stomach. Frequently they don't occur until sometime later after work, at night, or when relaxing. Heat cramps are caused by heavy sweating, especially when water is replaced by drinking, but not salt or potassium. Although heat cramps can be quite painful, they usually don't result in permanent damage. To prevent them, drink electrolyte solutions such as Gatorade during the day and try eating more fruits like bananas.

Heat Exhaustion

Heat exhaustion is more serious than heat cramps. It occurs when the body's internal air-conditioning system is overworked, but hasn't completely shut down. In heat exhaustion, the surface blood vessels and capillaries which originally enlarged to cool the blood collapse from loss of body fluids and necessary minerals. This happens when you don't drink enough fluids to replace what you're sweating away.

The symptoms of heat exhaustion include: headache, heavy sweating, intense thirst, dizziness, fatigue, loss of coordination, nausea, impaired judgment, loss of appetite, hyperventilation, tingling in hands or feet, anxiety, cool moist skin, weak and rapid pulse (120-200), and low to normal blood pressure.

Somebody suffering these symptoms should be moved to a cool location such as a shaded area or air-conditioned building. Have them lie down with their feet slightly elevated. Loosen their clothing, apply cool, wet cloths or fan them. Have them drink water or electrolyte drinks. Try to cool them down, and have them checked by medical personnel. Victims of heat exhaustion should avoid strenuous activity for at least a day, and they should continue to drink water to replace lost body fluids.

Heat Stroke

Heat stroke is a life threatening illness with a high death rate. It occurs when the body has depleted its supply of water and salt, and the victim's body temperature rises to deadly levels. A heat stroke victim may first suffer heat cramps and/or the heat exhaustion before progressing into the heat stroke stage, but this is not always the case. It should be noted that, on the job, heat stroke is sometimes mistaken for heart attack. It is therefore very important to be able to recognize the signs and symptoms of heat stroke - and to check for them anytime an employee collapses while working in a hot environment.

The early symptoms of heat stroke include a high body temperature (103 degrees F); a distinct absence of sweating (usually); hot red or flushed dry skin; rapid pulse; difficulty breathing; constricted pupils; any/all the signs or symptoms of heat exhaustion such as dizziness, headache, nausea, vomiting, or confusion, but more severe; bizarre behavior; and high blood pressure. Advance symptoms may be seizure or convulsions, collapse, loss of consciousness, and a body temperature of over 108° F.

It is vital to lower a heat stroke victim's body temperature. Seconds count. Pour water on them, fan them, or apply cold packs . Call 911 and get an ambulance on the way as soon as possible.

Information from an Oklahoma State University Environmental Health and Safety training series on heat stress.