If it’s not one thing, it’s another. We suffer through drought and heat, and then record rain. The other morning it felt decidedly fall-ish and now the humidity is almost unbearable. I’ve got loads of tomatoes on my plants but none of them are close to ripe. As hard as it is on people, it’s that hard on our plants and our lawns. We need to replenish the nutrients without encouraging too much growth. I’ve seen evidence of Japanese beetles on my roses and hibiscus. And on top of it all we now have diseases to control.
This time of year you need to be careful when applying chemicals. Chemicals are expensive and you want to be sure you get the most out of them. Your plants and lawn should be well watered before you apply any chemical. Chemicals can be stressful even on the non-target plant and you want them to be in the best condition before applying the chemical. Some chemicals work through the vascular system of the plant, like systemic insecticides or most herbicides. If the vascular system is not functioning because the plant is thirsty the chemical won’t work as effectively. In addition, many chemicals require that you not water for a day or two in order for the chemical to be fully taken in by the plant. If the plant or lawn is already dry, another day or two will stress it even further making the chemical less effective. You may think if the weed is going to die any way what does it matter. However if the weed can’t move the herbicide from the leaf to the roots it won’t work. We had a situation at work recently here a customer returned some Roundup because it wasn’t working. He had applied in the heat of July when the weeds weren’t actively growing so the weed wasn’t dying.
Most chemicals should not be applied when the temperature is over 85 . Again, heat causes plants to slow down their growth so the chemical won’t move through the plant efficiently. Over spray onto turf grass when you are trying to kill weeds in the lawn will stress the lawn. Most herbicides are taken in through the foliage by stomas or openings in the leaves. When the temperature rises, plants close these openings to conserve moisture. If the openings are closed, the chemical can’t be taken in.
Apply chemicals in the morning so that the chemical has a chance to dry before the sun hits it. Most chemicals have a petroleum based carrier. Those drops of chemical on the leaf can act like a magnifying glass, burning the leaf. If the leaf is damaged it cannot undergo photosynthesis as effectively. Photosynthesis is what produces the energy for the plant that is stored in the roots and helps the plant survive over the winter. When spraying insecticides, spray early in the morning when bees are not active so you don’t inadvertently kill them as well. Bees in the US have been under attack from Colony Collapse Disorder. Bees are responsible for the pollination of many of our agricultural production and the value of crop pollination is estimated to be $5-14 billion dollars according to a paper published in the Proceedings of the National Academy of Sciences. So do be careful when spraying insecticides as they are not selective and can’t tell a Japanese beetle from a bee.
Organic chemicals have become more popular, especially since more people are growing their own vegetables and herbs. Some of the most popular insecticides are neem oil (from the neem tree), pyrethrins (an extract from chrysanthemums), nicotine, sabadilla and rotenone. Neem oil also has a fungicidal effect. A new product on the market is a bacteria called spinosad which was discovered in the Caribbean in an old rum factory. Diatomaceous earth works great on crawling insects. Essentially it is shells of microscopic ocean dwelling animals called diatoms. Even microscopically the shells have very sharp edges. As the insects crawl over them is cuts them to shreds and they dehydrate. Sounds gruesome. For herbicides, organic controls include food grade oils (garlic, rosemary, etc.) and citric acid, usually in a soy based carrier. Most of these controls only kill the tops of the weed not the roots. They are also non selective, meaning you can’t use them to treat weeds in the lawn, but they are effective in killing weeds in the driveway, walkway, patio, or even in a flower bed if you are careful about overspray. Organic fungicides usually contain sulphur or copper.