Question: Last year my bermuda grass lawn seemed yellow in the spring so nitrogen fertilizer was applied. The lawn looked better but later in the summer it looked yellow again. Nitrogen was applied but the lawn was still yellow. Why the spring application of nitrogen work and the summer application did not?
Answer: Nitrogen is needed for fast spring growth. lron becomes less available in alkaline soils as the season progresses. Nitrogen deficiency shows up in older leaves that are yellow. Plants can break down nitrogen containing compounds and move it there the greatest need is, normally growing points, leaving older tissues yellow. On the other hand iron is used by plants to produce several compounds including chlorophyll. Plants cannot break down iron and move it to other parts of the plant. As the growing season progresses, alkaline soils bind iron and it becomes less available, so new leaves become chlorotic. Iron chlorosis has visual symptoms of green veins on new leaves but the interveinal spaces are yellow. Excessive watering can also cause iron chlorosis because soil oxygen pore space is filled with water. No oxygen-no root growth and little if any iron uptake.
Control: To correct iron deficiency, apply either ferrous sulphate, ferrous ammonium sulphate, or a chelated iron source to the lawn following label directions when first symptoms appear. Chelates are more expensive but will last longer than the other products, which will need to be applied more often. Usually two to four ounces of product are applied per 1,000 square feet. Mix the product with enough water to apply one to three gallons of water per 1,000 square feet of lawn area. Spray the lawn in the morning letting the spray dry all day long. Water the lawn before mowing. Excess iron spray will be stored in the soil and/or taken up by the turfgrass. Be careful not to stain concrete areas with the iron spray. Within a few days the turf should start greeningup.
Question: When my roses bloom they have brown and black petal edges and are deformed. Also the leaves are sticky. Some of the leaves are covered with yellow spots mixed with the green color of the leaves. What is causing these problems and what can I do?
Answer: Your roses have two insect problems and a virus. The flower petals are brown or black because of a very small insect called the western flower thrip, Frankliniella occidentalis (Pergande). Adult thrips are about 1/8", (2 mm), in length usually tan-to-dark brown bodied, with four feather like wings. The young or nymphs are creamy white and wingless and develop into adults in about two weeks. The adults enter a rose bud and lay eggs inside the immature flower. The eggs hatch and the resulting nymphs and adults injure the plant by rasping the bud, flower and leaf tissue of host plants and then suck the exuding sap. This causes petal tissue to die and results in brown or black petal edges, thrips also affect other flower, fruit and vegetable plants. These include apples and peaches which result in surface damage to the fruit. Onions, snap beans, chrysanthemums, gladiolus and iris are also damaged by other thrips species. There have been many more thrips the last couple of years because of the above normal rainfall which has provided abundant wildflower and weed crops for the thrips to live on and thus increased populations. The other insect problem is aphids. These small insects are yellow to green in color and suck sap from plants that they infect. The "sugars" which they do not metabolize are excreted and fall onto the leaves of the plant. This is the sticky, shiny substance that you see. Sometimes ants and flies will "milk" aphids for this exudate and feed on it. So if ants are spotted on plants there is a good chance that aphids are present. The yellow marks mixed with the green color of the leaves is a virus or a complex of several viruses. The spotted yellow-green leaf color is known as mottling and is very symptomatic of viruses. These viruses generally do not kill the plant but can weaken it.
Control: Several insects are predators of thrips and aphids. These include ladybird beetles and then larva, minute pirate bug and lacewings. Thrips have alternate hosts of weeds and wildflowers. By controlling host plants thrip populations will be lowered. Because thrips do damage inside the rose buds a systemic insecticide should be used. There are several products on the market which control thrips and aphids systemically. Sometimes disystox, a systemic insecticide, is included in rose fertilizer. Always follow label directions when applying pesticides. To reduce the problems of viruses in plants purchase virus-indexed or certified virus free plants. Virus infected plants can be a source of infection that can be transmitted to healthy plants by aphids or other insects. Therefore, control the aphids and other insects vectors to control the spread of virus diseases.
Source: Insect Pests of Farm, Garden and Orchard. 7th Ed. R. H. Davidson and W. F. Lyon. pp. 305-6,311-12.