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Weeds, Diseases, and Pests
Climate also affects the growth of pests and the spread of diseases. Since warmth, light and water are the main drivers for growth and development of insects and weeds, their distribution is influenced by climate.
Climate also affects the pesticides we use to control or prevent pest outbreaks. In a changing climate, pests are likely to become even more active than they are currently. Even though there are alternative ways to control pests, it is likely that farmers will use more and more harmful agricultural chemicals in the future. Increased use of these chemicals will be both ecologically and economically expensive.
Response to climate variables
In general, most pest species prefer warm and humid conditions. However a weak crop during a drought is more likely to become infected by a fungal infection than when it has enough water to be strong and healthy.
1. Using pesticides to protect crops.
Photo by USDA NRCS.
Rainfall, whether optimal, excessive, or insufficient, is probably the most important variable that affects the way in which plants are affected by pests or diseases. When there is too much or too little rain, it is really difficult to determine whether a drop in crop yield is due to the change in amount of water or due to pest infestation.
Pink rot, sometimes also called water rot, occurs occasionally wherever potatoes are grown. This disease is most serious when warm, wet soil conditions occur during tuber formation and at harvest, especially when the crop is grown in poorly drained soil.
2. Potato pink rot.
From The Ohio State University Extension Fact Sheet.
Pink rot is one of the most common diseases affecting potatoes. The name comes from the characteristic color the potato becomes when suffering from this disease.
Insects flourish in all climates. Their habitats and survival strategies are dependent on the local weather conditions, and, because they are cold blooded, insects are particularly sensitive to temperature changes.
Insects respond to higher temperatures by increasing the rate at which they reproduce. Warm winters reduce the number of insects which die over winter and, as a result, insect populations are higher in spring and summer. Abnormally cool, wet conditions can also bring on severe insect and plant infestations, although excessive soil moisture may drown insects which live in the soil.
3. Locust pest.
Picture from FAO.
The Desert Locust causes international problems. Frequent swarms of the locust travel huge distances from country to country destroying crops. Since the earliest records, this pest has been considered a serious threat to agricultural production in Africa, the Near East and Southwest Asia and often requires large-scale control operations.
Weeds compete with crops for soil nutrients, light, and space. Drought conditions increase competition for soil moisture between crops and weeds, while humid conditions increase the proliferation of weeds.
High temperatures and humidity result in the spread of diseases and influence the lifecycle of soil worms called nematodes. Some disease causing agents survive in hot, dry conditions as long as there is dew formation at night.
4. The Horsenettle weed which is commonly found in corn fields in the USA.
Photograph from the Mississippi agricultural and forestry experiment station.
As autumn approaches and corn begins to mature and dry ready for harvest, weeds take advantage of the available sunlight and grow at full speed. The Horsenettle is one of the most common weeds in corn in Mississippi and is extremely hard to eliminate.
About this page:
author: Marta Moneo and Dr. Ana Iglesias - Universidad Politécnica de Madrid, España
1. scientific reviewer: Alex de Sherbinin - CIESIN, Columbia University, USA
2. scientific reviewer: Lily Parshall - Goddard Institute for Space Studies, Columbia University, USA
educational reviewer: Emilio Sternfeld - Colegio Virgen de Mirasierra, España
last published: 2004-05-12