Applying Chemicals

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.

Using Garden Chemicals

Organic lawncare is less expensive in the long run but sometimes you have diseases or insects that require a chemical control or the weeds are running rampant and you just need to deal with them.  Garden chemicals are expensive but if you use them correctly they will be alot more effective and won't cost as much to use.

Before you spray make sure the plants, even the target weeds, are thoroughly watered in.  For the weeds, you want them actively growing so that they will take up all and use the herbicide more effectively.  Onamentals and vegetables should be actively growing so that they can withstand the stress of having chemicals applied to them.  Many chemicals require some period of no rain or water for the chemical to work its way into the plant. If the plant hasn't been watered before chemical application it may become stressed from lack of water.

Always spray when it is cool and expected to stay cool for a few days after application.  For herbicides this is especially important because plants take in the chemical through pores in their leaves.  In the heat these pores close up and the herbicide cannot be taken in by the plant.  Also, plants tend to slow down their rate of growth in the heat so if they are not actively growing they are not actively dying.  Leaves have a waxy coating or even a coating of dust that also impedes chemical takeup.  You can add a "spreader/sticker" to the chemical mixture that cuts through this wax and dirt and again increases the chemical's effectiveness.

Spray early in the morning so the chemical has time to dry before the sun hits it.  The beads of liquid can act like a magnifying glass and burn the leaves.  Spray when the wind is calm so that you don't have spray drift and accidently take out some of your perennials when you were spraying for other broad leaf weeds.

As always read the label and make sure it will treat the problem you have.  If you have questions about any chemical stop by Countryside and ask one the ICN professionals to help you determine what the problem is and how best to treat it.  And follow the label directions--more is not always better.

Using Chemicals

The party is over and now gardening is just work. There are many plants yet to bloom in the garden, but now we have to water, and deal with weeds and insect problems.


I found a few Japanese beetles on my asters, tho none on the roses yet. Last year I used Bayer Tree and Shrub systemic on the roses. It lasts for 12 months and it kept the beetles from chewing on the leaves but did not prevent them from eating the flowers. (In a side note, we wondered at a staff meeting if this meant using systemics on vegetables would be okay since if the chemical didn't get into the flower it wouldn't get into the fruit. I suggested an experiment but I couldn't get any volunteers. So don't try that at home, either.)


Whenever you apply chemicals it is really important to read the label and follow the directions. Make sure you water your plants thoroughly before applying the chemical. The chemicals are taken in through stomas on the plant leaf and move through the plant via its vascular system. If the plant is suffering from drought the chemical won't be as effective.

Since most chemicals have a petroleum-based carrier, apply the chemical either early in the morning or late in the evening, so that the chemical has a chance to dry before being hit by sunlight, otherwise you will burn the leaves and further stress the plant.


Heat can also affect how well the plant absorbs the chemical. When it is hot stomas close up to prevent moisture loss and chemicals sprayed when the temperature is over 85 degrees will not be as effectives as when sprayed when it is cooler.


Chemicals today are manufactured to use the least amount of chemical to get the maximum benefit. And they aren't cheap. So make the most of the money you spend on them by using them correctly and most effectively.