Japanese beetles - these pests will defoliate plants in short order. Keep a sharp lookout for them. If you find an infestation use carbaryl (Sevin, etc.), which is very effective. Observe all label precautions on mixing and use. Do not use dusts due to the problem with application - a spray made using the liquid form of the product will work fine. See Japanese Beetle for more information.
Fireblight - inspect fruit trees for fireblight. If you had problems with fireblight last year, you will need to spray your blooms this year to prevent the spread. The best defense is a fireblight-resistant variety. See Fireblight for more information.
Lawn diseases - it's time to begin watching for problems with brown patch and dollar spot in warm season grasses, especially if you had problems with one of them last year. See Brown Patch Disease of Lawns and Leaf Diseases of Lawns for more information.
Chinch bugs - watch for chinch bugs in your warm season lawn. See Chinch Bugs for more information.
White grubs - the bacteria Bacillus thuringiensis does a nice job on Japanese Beetle grubs, but it does take a little time to build up in the soil. Bacillus thuringiensis does not, however, control other types of grubs. See White Grub Management in Turfgrass for more information.
Bag worms - bag worms can kill a tree if it is heavily infested. Inspect your trees periodically - bagworms seem to like juniper, arborvitae, and pines, but they are will attack many broadleaf shrubs and trees such as rose, sycamore, maple, elm, and black locust.. Hand-picking light infestations works well; applying the bacteria Bacillus thuringiensis will also take care of the problem. See Bagworms for more information.
Oakworms - oakworms and canker worms may appear in the spring and defoliate oak trees. This will not kill the trees, but it will add some stress to them. The trees will develop more leaves. The chemical carbaryl (Sevin, etc.) will kill the worms, but treatment of a large tree is not practical nor safe and therefore is not recommended. However, if you have a small oak tree (less than 10 feet tall) infested with them that can be safely sprayed, an application of this insecticide will control them. The bacterium Bacillus thuringiensis (Dipel, etc.) will also control oakworms - and will not affect predatory insects. See Oak Diseases and Pests for more information.
Blossom end rot - check your tomatoes for blossom end rot on the fruit as it begins to form. This is usually an indication of a calcium deficiency. Place a handful of gypsum (land plaster) in the soil beside the tomato at planting (or later) to prevent this. Foliar sprays such as blossom end rot spray will also help alleviate the problem. Nothing will "heal" the fruit with rot on it, so remove and discard them. See Tomato for more information.
Things to do:
Bulbs - you should be planting your summer- and fall-flowering bulbs in April and May, such as dahlias, gladioli , cannas, and lilies. Be sure to plant after the soil temperature reaches 55 degrees F. See Summer- and Fall-Flowering Bulbs for more information
Spray fruit trees - continue spraying your fruit trees with a fungicide (Captan, etc.) every 7 to 10 days to provide the beautiful fruit you look forward to. Do not use any insecticides on the trees until less than 10% of the blooms remain - you certainly do not want to hurt your bee pollinators. The fungicide will have no effect on them.
Lawn Fertilizer - you should apply a complete fertilizer to your warm season lawn this month. See Fertilizing Lawns for more information.
Fire ants - if you broadcast baits, apply your first treatment during the last week of April or the first week few weeks of May. Be sure to apply fresh bait, and do it at the correct time of day (fire ants only forage actively when the ground temperature is between 70 and 95 degrees F). See Fire Ant Management in the Home Lawn for more information.
Lawn Aeration - any time your warm season lawn is actively growing is a good time to aerate. David Parker relates that you should "aerate as long as you can stand it, then go over the yard once more." See Aerating Lawns for more information.
Lawn Establishment - if you plan to plant a warm-season (centipede, zoysia, Bermuda, St. Augustine) lawn, the best time to plant is in the spring and summer. If you are planting Bermuda by seed, use the hulled seed at this time of year (you can seed with unhulled seed in the fall). Wait until next fall for cool-season grasses (fescue). See Lawn Establishment for more information.
Nutsedge or "nutgrass" - nutsedge is very difficult to control. There are two main types in our area - purple and yellow. You must identify which you have before you begin treatment. Herbicides must be applied when the nutsedge is actively growing, which means decent soil moisture and warm conditions. See Nutsedge for more information.
Irrigation - you may be irrigating late this month if we have a dry spring. See the Home and Garden Center's irrigation publications for more information, espcecially the publication on Irrigation Time of Day. Spring and fall are good times for disease to blossom, so do not allow your irrigation scheduling to increase these problems. One inch per week is the appropriate amount for most lawns and vegetables (except sweet corn and yellow squash, which may require up to two inches depending on growth stage). Include rainfall in this amount, and see How Much Water to determine how much water you are actually applying, and Determining When to Irrigate to help determine when your plants need water. Do not irrigate every day! There are a few exceptions to this rule (such as potted plants), but only a few.