HCS Extra Credit Report I will be going over three different crops and a major disease for each crop and describe the method to eliminate or prevent this disease. My three crops are corn, wheat, and soybeans. For corn the disease I will go over is diplodia stalk rot, for wheat the disease is rust, and for soybeans the disease is frogeye leaf spot. In corn, stalk rots are rather common and are usually the main corn disease problem. The development of stalk rot is best in good growing conditions earlier on in the growing season. The stalk rot I chose is diplodia stalk rot which is a soil borne stalk rot. Soil borne means that the pathogen remains in the soil and can remain there for several years. This infection starts in the root system of the plant, this infection can occur any time during the growing season but it usually occurs earlier in the growing season. The infection stays in the root not harming the plant until the plant starts its grain filling process. At this point the levels of carbohydrate in the stalk decrease significantly by the grain filling process of the plant. The natural stalk resistance is then basically depleted and the stalk rotting organisms move into the pith tissues from the roots. Rotting of the pith tissues causes the stalk to become weak and can make the plant susceptible to lodging. Symptoms of diplodia stalk rot usually do not show up until a few weeks after silking. Some infected plants may die prematurely, if this happens the plants will start to look grayish green, then the lower internodes become brown colored, and are easy to crush. The visible symptom of diplodia stalk rot is small black specks around the lower nodes. These specks are beneath the epidermis so a person is unable to scrape away these specks with just a finger nail, this is the difference between this disease and other stalk rot diseases. Also a white fungal growth may occur on the surface of the stalk in humid weather. The development of this stalk rot is most likely to occur in dry conditions early in the growing season followed by warm, wet conditions two to three weeks after silking has taken place. Some conditions that cause corn to be more susceptible to this stalk rot are high nitrogen, low potassium, large number of plant population, and early maturing hybrids are more likely to get it than full season hybrids. It is also said that this stalk rot is more severe in places where corn follows corn instead of in fields where crops are alternated each year. Diplodia stalk rot has been seen more in fields where corn follows corn and reduced tillage practices are used. There are many management methods for diplodia stalk rot. The best organic farming management methods for this disease are crop rotation, it is suggested to have at least one year out of corn due to the fact that the stalk rot is more severe in plants that are in fields that have had corn for more than on consecutive year. Other organic methods are to till the soil to break down crop residue, keep the fertility in the soil balanced, and decrease plant stress during growing season such as stress caused from insects, moisture, other diseases, and unbalanced nutrients. Since corn is more susceptible to this disease when plant population is high it is best to use moderate plant population if the field the corn is in is known for having stalk rot. Also a big management practice to prevent this stalk rot is to pick a good corn plant that has good genetic resistance to stalk rot, choose a plant with high scores for stalk strength. Another way to help prevent this from happening is to keep stalk boring insects from harming the plant and giving the disease organisms openings in the stalk to infect it easier, according to the Pioneer website two Pioneer brand hybrids are Herculex I or Herculex Xtra with good insect protection traits. “There are three rust diseases that occur on wheat: stem rust, leaf rust and stripe rust. These diseases are each
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Arizona Controlled Environment Agriculture Center 1951 E. Roger Road Tucson, AZ 85719 Revised December, 2012
TABLE OF CONTENTS
CHAPTER 1: Controlled Environment Agriculture and Hydroponics: Past, Present and Future The Plant How to grow greenhouse crops Plant Protection: Insects and Diseases Basic Principals of Hydroponics Transplant Production Pollination, Fertilization and Bee Management Fruit Harvesting, Grading and Storage Plant Nutrition and Nutritional Disorders Fertigation Systems and Nutrient…