Creating a Balance - Garden Sanitation vs. Beneficial Insect Habitat in the Home Landscape

Many gardeners are starting their fall garden and landscape clean-up - which is good and bad. Garden sanitation, if insects or diseases were a problem this year, is an important step to reduce problems next year. But we need to balance pest control with allowing habitat for beneficial insects and pollinators. So, how can that be done? 

Clean Up for Problem Plants
Many disease organisms carry over from one season to the next on infected branches, leaves or fruits. Diseased leaves fall to the ground beneath the infected plant and, if they are not removed and discarded, will produce new fungal spores or bacteria to reinfect plants the following growing season. Removing infected plant debris reduces the disease pressure the following season. Keep this control method in mind for common shade tree foliage infections, including Anthracnose, powdery mildew, apple scab, Septoria and many other leaf spot pathogens. Black spot of rose is another very common fungal pathogen.

In a similar manner, fruit tree disease problems often overwinter on fruit "mummies"; dried infected fruits that may remain in the tree or fall to the ground beneath the tree. If mummies are still in the tree or beneath it, they serve as an infection source the following year.

Diseases also remain active from year to year through infected twigs, branches or cankers. Fireblight is one of the most serious fruit and ornamental diseases which overwinters on infected woody tissue. Fireblight is a bacterial disease which infects and kills twigs and branches, most commonly during spring and early summer. However, it can also infect the mature bark of older branches or tree trunks; this infected bark is called a canker and often serves as a source of additional spores or bacteria, allowing the disease to progress throughout the plant during a growing season or reinfect its foliage or new branches in future years. Unfortunately there are many other disease pathogens that can infect woody branches or bark and cause cankers, such as brown rot of peach, apricot, plum and cherry.

Many insects overwinter on plants they attacked the previous summer or nearby plant debris, such as iris borer (overwinter as eggs on iris leaves or nearby plants) or common stalk borers (overwinter as eggs on nearby grass stems or weeds).  Cucumber beetles overwinter as adults in plant debris and other protected areas. Common fruit insects – plum curculio overwinters as adults in plant debris, cherry fruit fly inside fallen fruits.

Sanitation Steps
In areas where insects/diseases were a problem this year, sanitation is very important for reducing disease and insect pressure in your garden or landscape each year. Important steps include the following. 

1.     Rake up and discard or burn all debris beneath infected plants each fall, including leaves and fruit.  This includes infected trees, shrubs and ornamentals such as peonies. In the vegetable garden, remove any disease infected plants like tomatoes or peppers and rake up as much old foliage as possible along with all discarded fruits.

2.     Prune out and destroy all dead or diseased branches and twigs each spring. Dead or diseased branches can be pruned out at any time of year. If you suspect the branches were killed by a disease, cuts should be made at least 4-6 inches below the margin of visible infection.

3.     If your tree is susceptible to fireblight or has a history of infections and you are pruning before the tree is fully dormant, be sure to clean the pruners between each cut. Clean pruners by dipping them in a 10% bleach solution (9 parts water to 1 part bleach) between cuts. With a known fireblight infection, make cuts 8-12 inches below the margin of visible infection. Dry and oil tools after use to prevent rust.

4.     In Iris plantings, remove old dead foliage before April 1.

5.     Black spot of rose can be reduced by removing all infected leaves and mulch beneath plants in fall. Prune out canes with dark colored lesions, then reapply a fresh layer of new mulch.

6.     Do not compost this material, because most home compost piles do not get hot enough to kill all pathogens.

But Don’t Be a Neat Freak 
To achieve a good balance for beneficial insect habitat, don't be a neat freak in all the other areas of your landscape where insects and diseases were not a problem. Consider allowing your gardens to have a slightly more natural, unmanicured look. Getting rid of all that leaf debris is not only a waste of good organic material, it decreases your population of beneficial insects.   

For example, luna moths lay eggs on a variety of trees, including black walnut, willow, sumac and white birch. They overwinter as cocoons, which can often be found beneath these trees and could be discarded or killed during fall clean-up. Praying mantids overwinter as eggs in a dried papery egg mass on plant stems. Fireflies, lady bugs, spider mite destroyers, ground beetles and many other beneficial insects hide in protected leaf litter during winter.    A thick wood chip mulch layer is difficult for ground-nesting bees to dig through to reach the soil beneath; this reduces the potential for these bee species to make their home in your landscape. Leaf litter is easier for them to dig through, so creates better habitat.      Consider using existing leaf litter as your mulch or only mulching a few feet at the front of your gardens in the most visible areas. Allow the back of beds, which are less visible, to remain covered by a natural mulch of leaf and plant debris.    Cut Down Stems – Part Way  Many gardeners know leaving dead flower stalks standing over winter, is a good practice. Standing stems catch snow, resulting in moisture for the plant when the snow melts. So, instead of cutting perennials back to the ground in fall, ideally allow them to stand until spring. If you can't do that, then cut them back part way using staggered heights ranging from 8-24 inches.  The hollow stems are also used by many bees species as overwintering sites, such as leafcutter, carder, mason and species of smaller carpenter bees, potter wasps and many more. Allowing stems to stand will protect any overwinter insects inside until they emerge. The infographic below, from The Ohio State University, gives a good overview of how to maintain garden perennials while maintaining good bee habitat.     How to Create Habitat for Stem-nesting Bees.   If the garden doesn’t look neat enough when you’re done, lightly top dress with mulch. This will hold any leaves or debris in place, reducing the potential of it blowing out of your beds. Just don’t put it on too thickly if you’re trying to maximize habitat for ground-nesting bees.     When you’re done, you’ll have accomplished three important tasks. 

1. Neat garden beds ready for winter. 
2. Management of next year's insect/disease problems,
3. Maintained great habitat for bees, pollinators and other beneficial insects.  

Great work! Give yourself a pat on the back and go have a beverage. 

 

Images

1. Black spot on rose, William Fountain, University of Kentucky, Bugwood.org
2. Hollow stems of grasses and perennials in the garden can be used by many bee species as nesting and overwintering sites. Pixabay.com.