How to control blackspot on roses and grubs in lawns

I do not see many hybrid tea or floribunda roses in home gardens. These types of roses need some extra care to perform well. Deadhead hybrid roses as soon as the flowers fade. Many shrub roses are self-cleaning and don’t require deadheading. When in doubt, lightly prune old blossoms to keep plants looking attractive. Do not deadhead any roses that are being grown for their hip production.

If your hybrid roses have been losing their lower leaves and remaining leaves have yellowish foliage with dark spots, it is likely your roses are infected with blackspot, which is a common fungal disease. Begin a spray program with approved fungicides immediately. The fungicides need to be applied once every seven to 10 days, since they work to prevent the disease and do not cure what is already infected. Be sure to clean up any leaves that have fallen from the plants. Most landscape shrub roses are resistant to black spot and do not need to be on a spray program. Landscape roses also do not need extra winter protection. Do not spray Rosa rugosa as the fungicides used to control blackspot can burn the foliage.

Grubs can be a problem in lawns some years. For their egg-laying in early summer, the adult beetles are attracted to irrigated lawns that are surrounded by dry lawns. If the season is dry and you are the only one on the block watering your lawn, you will have a greater chance of having grubs. Do not automatically treat for grubs, though, because your lawn may or may not have a problem this year.

Typically, when there are eight to 12 grubs per square foot, visible damage will occur as they feed on the roots of the grass. The lawn will brown out later in the season when hot and dry weather increases stress on the lawn. Raccoons and skunks dig in lawns for the grubs, and this is often the first sign that grubs are present. If you plan to use a fungicide, be sure to read the label carefully to make sure you are using the right product at the right time of year. Products designed to prevent grubs are generally applied from late June to mid-July.

There are products designed for quick kill of grubs that are applied later in the season when grubs reach a threshold in the lawn that is causing damage and you see the results. There is no need to control a small number of grubs that the lawn can withstand. I do not water my own lawn nor apply any grub controls and have never had a problem with grubs causing any noticeable damage to my turf, only minor damage that most would not notice.

• Tim Johnson is director of horticulture at Chicago Botanic Garden, chicagobotanic.org.