Guess the Pest! Week #9 Answer: Plum Curculio

Bill Cissel, Extension Agent – Integrated Pest Management; bcissel@udel.edu

Congratulations to Sylvie Childress for correctly identifying the ovipositioning scar and larva in the photos below as plum curculio and for being selected to be entered into the end of season raffle for $100 not once but five times. Everyone else who guessed correctly will also have their name entered into the raffle. Click on the Guess the Pest logo to participate in this week’s Guess the Pest challenge!

Guess the Pest Week #9 Answer: Plum Curculio

The plum curculio is a pest of apples, peaches, plum, and other stone fruit. The adult beetles are about ¼” in length, dark brown with patches of white, and have a protruding snout. They belong to the weevil family, commonly referred to as the snout beetles.

Adult Plum Curculio

The primary damage to fruit is caused by the ovipositioning or egg laying behavior of the female plum curculio. The females lay eggs in the developing fruit and cut a crescent shaped slit beneath each egg to prevent the rapidly growing fruit from crushing the egg. As the fruit continues to grow, the slit the female beetle cut below the egg develops into the classic, crescent shaped scar that you see in the photo above. These scars are usually only cosmetic. However, if the egg hatches, the larva will bore into the fruit, which will usually cause the fruit to drop from the tree. After a couple weeks of feeding on the fruit, the larva will exit the fruit to pupate in the soil.

In addition to the crescent shaped ovipositioning scars and fruit drop, the adult beetles will also feed on fruit, creating numerous round puncture holes in the fruit skin. It has been estimated that a single beetle will average over 100 feeding and/or puncture wounds during its lifespan.

Fun Entomology Fact: The family Curculionidae (true weevils), are the largest family of insects with the most species described worldwide.

False Spring Concerns – Again

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

Some peaches, nectarines, plums, and apricots have started to bloom — four weeks ahead of normal. Other fruits such as strawberries may be blooming ahead of schedule in plasticulture systems. These fruit crops are at great risk of losses due to freeze events. Other fruits such as pears, cherries, and blueberries may also flower early and be at risk.

The expected temperatures near 20°F at the end of this week will damage many of these flowers. The long range outlook for March and April shows a return to more seasonable weather which will slow bloom. However, crops already in bloom will be exposed to the potential of freezing temperatures throughout the rest of March and April.

Peach in various stages of flowering including open bloom, the most susceptible state to freeze damage on March 2, 2017.

Open nectarine flower on March 2, 2017.

Plum with high percentage of open flowers on March 2, 2017

Pluot in full flower on March 2, 2017.

Normally, the average date of the last frost in Delaware is somewhere between April 20-25. We still have seven weeks of worry ahead for our fruiting crops.

For all these fruit crops the most susceptible stage of injury is when flowers have just opened. Open blooms are damaged at 32-34° F. Blooms prior to opening have higher cold tolerance as do small fruit. For most fruits, critical temperature for losses after fruits have formed is 28-30° F.

Frost and freeze protection methods vary with fruits and the type of freeze expected. Advective freezes occur with freezing temperatures and high winds. This is the most difficult to protect against. For strawberries, two layers of floating row covers may be the most effective strategy for advective freezes. Double covers have been shown to be more effective than single heavy covers in this case. Irrigation along with double covers can provide even more protection if done properly.

Radiation (or radiant) freezes occur on cold, still nights. In this case cold air is near the ground and warmer air is above. Wind machines and helicopters have been successfully used to stir the air and raise the temperatures in orchards in this case. Row covers in strawberries will protect against radiation freezes too. Other options are over the top sprinklers, ground sprinklers, and heaters.

Over the top sprinkling is commonly used for frost protection but it has to be done properly. How this works is that as clear ice forms on plants heat is released. For frost production, overhead sprinkler systems are designed to deliver 0.1 to 0.2 acre-inches of water per hour. This method is used for radiant freeze or frost protection when wind speeds are low and temperatures 24°F or above. The key is to keep ice formation occurring through the night and continue through melt in the morning. Remember that initially, until ice starts forming, there will be evaporative cooling of the plant. The latent heat of fusion (water freezing) will release heat (approximately 144 BTUs/lb of water), whereas evaporative cooling will absorb heat from the plant (absorbing approximately 1,044 BTUs/lb of water) and lower plant temperatures. Therefore, irrigation must start well above critical temperatures. Also, the volume of water needed needs to be matched with the expected temperature drop and wind speed. In addition, uniformity of water application is critical. This is difficult to do in high wind situations. In orchards, under-tree sprinklers can also be used to release heat (hot air then rises, protecting blooms).

Heaters that are placed throughout an orchard will add heat. Large numbers of small heaters are preferred (40 per acre). This is accomplished with fuel oil fired heaters, gas/propane heaters, or burn barrels using wood or other fuel (check with regulatory agencies before using open burning in barrels). Heaters are much more efficient and less are required if they are used in conjunction with wind machines.

Wind machines or frost protection fans above an orchard or vineyard mix the warmer air above the inversion layer with the colder air at ground level to protect against radiation frosts. These large fans can be permanently installed and will cover as much as 10 acres. Another type of fan is placed at ground level and pushes the cold air upward, again achieving mixing. Portable fans are also available.

The following is a good factsheet on frost protection on berry crops: http://www.fruit.cornell.edu/berry/production/pdfs/frost%20protection%20tips%20techniques.pdf

Freezes, Frost and Frost/Freeze Protection

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

Fruits and fruit flowers are damaged by temperatures below 28°F and by frost. Temperatures in Delaware reached 21°F or lower on April 6. Another freeze is predicted for Saturday, April 9. The term freeze means that temperatures dropped below 32°F. Frost is the formation of ice crystals on crops and occurs when the dew point is near or below freezing. You can have a freeze without frost and a frost without a freeze. Both are damaging to plant tissue.

Frost and freeze protection methods vary with fruits and the type of freeze expected. Advective freezes occur with freezing temperatures and high winds. This is the most difficult to protect against. For strawberries, two layers of floating row covers may be the most effective strategy for advective freezes. Double covers have been shown to be more effective than single heavy covers in this case. Irrigation along with double covers can provide even more protection if done properly.

Radiational freezes occur on cold, still nights. In this case cold air is near the ground and warmer air is above. Wind machines and helicopters have been successfully used to stir the air and raise the temperatures in orchards in this case. Row covers in strawberries will protect against radiational freezes too.

Irrigation has also been successfully used for frost protection but it has to be done properly. How irrigation works is that as ice forms on plants heat is released. The key is to keep ice formation occurring through the night and continue through melt in the morning. Remember that initially, until ice starts forming, there will actually be evaporative cooling of the plant. The latent heat of fusion (water freezing) will release heat (approximately 144 BTUs/lb of water), whereas evaporative cooling will absorb heat from the plant (absorbing approximately 1,044 BTUs/lb of water) and lower plant temperatures. Therefore, irrigation must start well above critical temperatures. Also, the volume of water needed needs to be matched with the expected temperature drop and wind speed. In addition, uniformity of water application is critical. This is difficult to do in high wind situations.

Site Selection for Fruit Plantings

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

There has been an increase in interest in planting fruits in Delaware. This is a positive trend that matches the interest in buying local and can also provide local fruit to the steady influx of visitors in the region.

Success with tree fruits, blueberries, grapes, brambles, and other long-term perennial fruits begins with selecting a proper site. I have visited too many sites in the past 10 years where growers have lost expensive planting material because of poor locations and poor planning. Landowners most often are not buying properties with fruit planting in mind and many properties just are not suitable for fruit.

The most common issue with planting fruit is that of high seasonal water tables. When water rises in winter, it can saturate part of the root zone of the fruit plant and roots will then die due to lack of oxygen. Roots injured by waterlogging are also then more susceptible to root rot pathogens. Fruit plants with water damaged roots also have fewer effective roots which can make them more susceptible to other plant stresses such as drought. In the end, these fruit plants will die prematurely, have shorter life spans or will be less productive.

The best time to evaluate a site for the height of the seasonal water table is in late winter. Find the lowest elevation in the property being evaluated and dig a hole 6 feet deep using a posthole digger. If any free water is found in the hole then the site is not suitable for most deep rooted perennial fruits such as tree fruits and grapes. With brambles and blueberries water should not be found within 4-5 feet of the surface in these observation holes. Also examine the soil that comes out of the borings. If you see considerable amount of gray colored soil, this is an indication of water saturation. Do these borings throughout the property and map your site and avoid planting fruits on any areas with high water tables.

Another problem with water saturation and roots can be perched water tables. This is when an impervious soil layer does not allow water to drain and a saturated area develops above that layer. If perched water tables are found, the area is again not ideally suited for fruits. Subsoiling can fracture these layers if done properly but the layers may reform in a few years.

In high water table soils, it may be possible to grow some fruits such as brambles or blueberries by creating high mounds to grow on. In this case, the growing area is elevated 2-4 feet by moving soil to create a mounded ridge where fruit is planted. While this is possible, it is expensive and must be done in such a way that water does not collect between the mounds.

Another issue with fruit siting is air drainage. Our last 2 winters have had sub-zero conditions which can cause problems with winter kill in some grapes and brambles and bud damage in some tree fruits. Lower areas where cold air drains to also are more susceptible to late frost damage to flowers in the spring, particularly in peaches, nectarines, apricots, and plums. All sites should be evaluated for air drainage by doing elevations on the property. Fruit should be planted on the highest elevations and frost pockets should be avoided. Frost pockets are easily seen by looking where frost is found during late spring frost events. On Delmarva, an issue we have is that some areas are just completely flat, with low elevation. These areas will not allow for air to drain and can also have issues with cold air accumulating.

Soil pH is an issue with blueberry establishment. Blueberries require a soil pH of 4.5-4.8. Most of our soils have much higher pHs and the soil must be acidified before blueberries can be planted. This can take 1-2 years using sulfur as the acidifying agent.

Sites should also be evaluated for nematodes, soil pests that can be damaging to fruit roots, before planting.

Section 18 Label for Brown Marmorated Stink Bug (BMSB) Management in Stone and Pome Fruit

Joanne Whalen, Extension IPM Specialist; jwhalen@udel.edu

We just received the notice that our Section 18 request for the use of two dinotefuran products (Trade Names: Venom from Valent U.S.A. Corporation; and Scorpion 35SL from Gowan Company, LLC) to control BMSB on stone and pome fruits has been approved by EPA. This use expires on Oct 15, 2015. You must have a copy of the label in your possession before making an application. The labels contain information on use rate, restrictions, PHI and REI as well as information on pollinator protection. Please contact either Christopher Wade at the Delaware Department of Agriculture (Christopher.Wade@state.de.us) or Joanne Whalen (jwhalen@udel.edu) for more information.

Winter Injury in Fruits

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

We are finally seeing bloom in fruit crops. Plums and apricots are in mid-bloom, peaches and nectarines are just starting to bloom. This is about 2 weeks later than the average.

As bloom occurs, winter damage to buds will become evident. Cold susceptible plants such as blueberries, wine grapes, peaches, blackberries and nectarines can have bud damage when winter temperatures drop below -10°F. There is a lot of variation between grape varieties. Many of the European wine grapes will have damage between zero and -10 F, hybrids and American types can withstand lower temperatures. Other fruits are more cold-hardy. Cherries and European plums can withstand -20 to -25°F and apples and pears go to -25°F without damage. Delaware had temperatures approaching -10°F in some areas. Initial observations indicate that sensitive peach and grape varieties have bud damage.

Fruits that were under stress in 2013 may also show more winter injury. We had significant water damage in lower areas of fields last year and trees, vines, or canes with root damage from waterlogging may also have increased winter injury. Trees with high or excessive fruit loads in 2013 may also show increased winter damage.

Wet Season Fruit Problems

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

It has been a wet week and excess moisture can cause problems in fruit crops. It has been so wet that during blackberry harvest we are seeing slugs on ripe fruit (we even saw some slugs on blueberries!). While slugs are not a normal problem in fruit, excess moisture is a problem in some years. Currently, brambles (raspberries and blackberries), blueberries, peaches, plums, and apricots are being harvested. Cherry season is past but we did have wet weather during cherry harvest.

Of the fruit crops, sweet cherries are the most sensitive to excess moisture. Cracking due to excess moisture is a major reason that we have problems growing sweet cherries on Delmarva. It is not the uptake of water through the plant root system that causes the cracking; it is the absorption of water through the cherry fruit cuticle that causes the fruit splitting. The theory is that as a cherry nears ripening with the accumulation of sugars, cherry fruit exposed to extended periods of wetness from rain, dew, or high humidity conditions will absorb water through the fruit skin and swell until the fruit cracks. Some cherry varieties are more susceptible to cracking than others.

Growers of sweet cherries in the east often lose large portions of their crop due to fruit cracking. In the past, the tools that growers have used are to physically remove water from cherry fruit surfaces using helicopters or blower sprayers. Use of Calcium Chloride sprays prior to rain events acts to reduce the osmotic potential of rain water. Chemical barriers have also been tried to prevent water movement into the fruit with varying success.

There has been great interest in the use of high tunnels with dwarf sweet cherries to control cracking by eliminating wetness on fruit surfaces with these plastic covers. There is a new planting of dwarf sweet cherries in a high tunnel at T.S. Smith and Sons in Bridgeville, DE as a part of a Specialty Crop Block Grant from the Delaware Department of Agriculture. We will be holding workshops on this production technique over the next 3 years.

Similar skin cracking can occur in nectarines, plums, and peaches. When the skin of these fruits stays wet for an extended period near ripening, the fruit can absorb so much moisture that it also cracks. This is a problem for growers that do “tree ripe” fruit. Earlier harvest and ripening off the tree can help control this problem.

Some blueberry varieties are also susceptible to fruit cracking at ripening. Research has shown that both fruit absorption of water and internal water accumulation from root uptake cause this cracking.

Section 18 for Brown Marmorated Stink Bug (BMSB) Management on Stone and Pome Fruit

In an earlier newsletter, we said we would also post the Scorpion Section 18 label as soon as it is available. Here is the label that you will need in your possession to use: Scorpion Section 18 Label for BMSB in Pome and Stone Fruit. Please refer to past newsletters for links to the Venom Section 18 label (June 7) as well as the Bifenture Section 18 labels (June 14). We will post the Brigade WSB label as soon as it is available. Please contact either David Pyne at the Delaware Department of Agriculture (David.Pyne@state.de.us) or Joanne Whalen (jwhalen@udel.edu) for more information.

Fruit Drop in Tree Fruits

Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu

Fruit trees commonly set more fruit than they will carry and chemical, mechanical, or hand thinning is done to reduce fruit loads, increase fruit size, and limit alternate year bearing. Natural fruit drop also occurs and is often called “May Drop” or “June Drop”. This is often accompanied by some leaf drop, especially in stone fruits.

Natural fruit drop is a result of unfertilized or poorly fertilized seeds, cold injury, competition between fruits, or shading. Poor pollination may be a result of cold, rainy weather during bloom in self-fertile fruits such as peaches or poor insect pollinator activity during flowering in insect pollinated fruits such as apples. In stone fruit, some fruit that is not fertilized will remain on the plant for 25-50 days after bloom and then will drop before pit hardening starts.

Another wave of natural fruit drop occurs in late May or early June. This fruit drop is due to competition between fruit for sugars stored and produced by the tree. A tree can only carry a certain load of fruit and will naturally drop smaller and weaker fruit during this period. However, thinning should have been accomplished before this competitive fruit drop occurs. Having fruit remain on the plant until natural competitive drop will use up food reserves in the plant and reduce the size potential of remaining fruit. Fewer cells will have been produced by the fruit remaining on the plant and therefore fruit size will not be recovered.

Another cause of fruit drop is cloudy weather during the period 5 to 7 weeks after bloom. A continuous 4 day period of cloudy days during this period will also cause fruit to drop. In addition, defoliation due to disease such as peach leaf curl, chemical injury such as copper fungicide damage, or severe storms can cause fruit drop during this critical period.