Plant and Insect Diagnostic Clinic Update – July 10, 2020

The following are highlights and updates about digital and sample submissions for our different services (identification or Plant problem diagnosis from fruit, vegetables, and ornamentals), and questions recently received in the Plant and Insect Diagnostic Clinic.

We are providing digital diagnostics mainly and requesting samples for testing when we deem it critical. We are operating at reduced capacity. Our building is locked to the public. see our guidelines at

Visit the PIDC's Facebook page for updates and more pictures. For more information on a particular disease or insect problem listed, follow the article cited.

Plant Problem diagnosis  (with links to articles)

Broadleaf Trees

Anything you can do to promote vigor can help trees to thrive. Consider removing the turf from below the trees and install arborist chip mulch to improve overall health. Otherwise, the tree has to compete with your turf for water. See more information at the Tree and Shrub page.

Oak, MapleDecline, Nutrient deficiency
Oak, hackberryTatters
OaksTubakia leaf spotAnthracnose, Bot twig canker and dieback
Oak, Catalpa, Maple

Transplant shock/stress, plated too deep, Poor Planting Practices and Post-planting Care

Drought stress, sunscald/leaf scorch

ElmDutch elm disease suspected
MapleVerticillium wilt suspected

Coniferous Trees

ArborvitaeFletcher scale, Spider mite damage
SpruceStigmina needle castDiplodia Tip Blight and Canker,  Rhizosphaera needlecast
Juniper, SpruceSpider mite damage 
Austrian pine, Scots PineDothistroma needle blight
Scots PineLophodermium needle blight suspected


Drip irrigation (using a soaker hose) or directing the hose nozzle as close to the crown of the plant (soil level) can help minimize unnecessary moisture in the leaves and stems. Remember plant pathogens take advantage of excess moisture to reproduce, and water splash to spread.

Cucurbits (squash and pumpkin)Angular Leaf Spot, anthracnose, powdery mildew

Early blight, various virus, Physiological leaf curl, 

see Tomato Diseases and Disorders

Various vegetables,

especially Tomatoes

Suspected herbicide injury, see article:

Understanding and preventing herbicide injury

OnionPurple blotch
GarlicFusarium Basal rot, virus.


Managing disease in the home orchard takes an integrated approach. From proper pruning and care, to considering fungicide sprays to prevent fruit diseases. Good pruning practices can help reduce the places where pathogen hides (cankers in wood/limbs), while also increasing airflow and minimize moisture that is necessary for plant pathogens to thrive. See the free to download publication Pruning and Training Fruit Trees on

Frog eye leaf spot/ black rot symptoms in apple leaves
Frog eye leaf spot/ black rot symptoms in apple leaves
AppleFrog eye leaf spot/ black rot, Cedar-Apple Rust, aphid, decline, spray phytotoxicity, 
Pear, AppleFire Blight, fungal cankers
PeachPeach leaf curl, wood decay fungi, decline
Peach, cherryGummosis
Raspberrycane/spur blight 
StrawberryBlack Root Rot

Perennials and Annuals

HollyhockHollyhock rust
PeonyPeony leaf blotch
HostaSunscald, Anthracnose, leaf spot, virus 
Various host 

Chemical injury suspected,

see article preventing herbicide injury  in the landscape

Preventative application of fungicides can help minimize damage to fruit these two publications have very good information including sprays: Managing Pests in Home Fruit Plantings (Purdue University) and Fruit Spray Schedules for the Homeowner (University of Missouri).


Smut, Slime mold, brown patch, leaf spot melting out

Best practices for irrigating your lawn to minimize disease problems:

  • Most lawns may only need to be watered under heat and drought conditions (4-6 wks of dry conditions)
  • Water early in the morning (4am- 8am), this will mean less water will evaporate, more water to the root system!
  • Water infrequently but deeply! meaning turf should be irrigated with 1 to 1-1/2 inches of water in one thorough irrigation. More on lawn irrigation in the publication Irrigation practices for Homeowners


Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Horticulture and Home Pest News, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on July 10, 2020. The information contained within may not be the most current and accurate depending on when it is accessed.