Diagnosing Plant Problems - Frequently Asked Questions

 
 
Subscribe to our free E-Newsletter, "Agri-News" (formerly RTW This Week)Agri-News
This Week
 
 
 
 Each growing season problems arise that affect the health and productivity of various crops. Producers inevitably want to know “What can they do about it?” Prior to correcting the problem it is critical to correctly identify the cause. This is accomplished by asking many questions, with the purpose of gathering enough information to correctly understand the probable cause and then make decisions to fix the problem (or realistically reduce the problem or prevent more damage from occurring).

Scouting for potential problems should take place regularly, in field (not from the truck cab at 100 km/hr). Scouting should take place pre-seeding, pre & post-spraying and pre & post-harvest. It is also important to be aware of potential pests and scout more during periods of high risk for specific pests.

The process of diagnosing a problem is a process of elimination and can resemble peeling an onion. A series of questions must be asked, with each question designed to reveal more information. The flow of questions may follow several courses, with the end result a clear grasp of all relevant factors. Failure to gather all pertinent information can lead to misdiagnosis. It is possible that information gathered in earlier questions might provide a clue to the cause of the problem. It is also possible that several factors may be related.

What is the crop?

  • What crop is it?
  • What is the variety?
  • Is it the only crop that is affected?
  • What is the growth stage of the crop?
  • If it is a perennial crop, how old is the stand or what production year is it?
What is the extent of the problem in the field?
  • Is this an isolated case in the field?
  • If there are several plants affected, are they in groups (clumps), in rows or sporadically located?
  • Is there a pattern? Is it in a clump in a low area, in a wave pattern, coming in from the side of the field or an overlap, miss, heavy weed patch, bare patch? Consider the equipment type and set up.
  • Does the problem appear to be spreading?
What is the field like?
  • Does the problem appear in a low spot, next to a windbreak or shelterbelt, on a knoll, in the field entrances or close to the field margins?
  • Does the problem appear in an area where there was lots of manure applied in the past, in a saline area, etc?
  • What is the weed situation like in the field? What are the predominant weed species? Does the problem occur near a heavy patch of weeds?
What are the environmental conditions like (past/present)?
  • What has the weather been like lately? Hot and dry, hot and humid, cool and wet, cool and windy? Consider both daytime and nighttime.
  • Have there been any frosts or other sudden temperature shifts lately?
  • What is your water situation? What has the growing season precipitation been recently?
  • What was the spring soil moisture level?
  • Is there excess water in the area?
What are the agricultural practices?
  • Do you soil test? What is your soil fertility?
  • Do you fertilize to the potential of each crop?
  • When you most recently applied fertilizer, what and how much did you apply?
  • Have you applied manure? How much? What was the quality of the manure? Was it composted?
  • Do you have irrigation?
  • If you have irrigation, how much do you irrigate, when do you irrigate, what type of irrigation system do you have? What is the water quality?
  • How much tillage do you do?
  • What is your management level? Have you done any type of management recently (e.g. pruning, tillage, spraying, etc.)?
  • When did seeding take place? At what rate? What were conditions like at the time?
  • Was a seed germination &/or seed vigour test done?
  • If applicable, did you use an inoculant?
  • Did you use a seed treatment?
  • What is the weed situation in the field?
What are the general symptoms?
  • When do the symptoms occur?
  • Where do the symptoms occur?
  • Are the plants distorted (as if by chemical damage)?
  • Are lesions present?
  • Does there appear to be any evidence of insects or insect damage?
Depending on the answers to these questions, more specific questions would need to be asked regarding disease, insect or herbicide damage.

If a disease is suspected, “What should I look for?”
  • What plant parts are affected?
  • What is the appearance of the disease?
  • Is there an obvious mould present and what colour is it?
  • Are there lesions on the plant? Are they near the nodes, at the crown, near the inflorescence, on the fruit?
  • If there are lesions present, what do they look like? Are they defined or do they spread randomly across the tissues? Do they have a different coloured margin?
  • Are there fungal fruiting structures present? What do they look like?
  • Is the plant wilting? Dig up the plant to keep the roots intact.
  • How do the roots look? Are they discoloured? If Yes, what colour are they? How is the root structure? Are there any other root symptoms?
  • Are there any other symptoms that seem out of place?
If an insect is suspected, “What should I look for?”
  • Are there any insects present? If yes, describe them and what they are doing and/or take a picture of them. More detail is better.
  • If no insects are apparent, is there any evidence that insects may be present (e.g. frass, chewed areas, skins, etc.)?
  • What plant parts are damaged?
  • Depending on what plant part is affected, attempt to dislodge or find any insects. This may involve digging in the top of the soil.
If herbicide damage is suspected, “What should I look for?”
  • Is the plant distorted or growing abnormally?
  • Is the whole plant dead?
  • Is there tissue death (from the margins or other)
  • What pesticides have been sprayed on the land this year? Last year? The year before that?
  • What crops were grown on the land in the past years? What is the crop/field history?
  • Do they follow a rotation?
  • What crops have been grown on adjacent properties in the last few years?
  • What pesticides have been sprayed on the adjacent property?
  • Has the county recently sprayed the ditches or right-of-ways?
  • Consider the level of moisture in the recent past (1-2 years). This can affect herbicide breakdown in the soil.
  • Has a field bioassay, tissue test or water test been conducted?
What do I do if there is still uncertainty about the diagnosis?
In many cases, problems cannot be definitively identified solely by consideration of visual symptoms and descriptive information. Samples may need to be collected and submitted to a diagnostic laboratory for analysis.

Prepared by Robert Spencer, Ag-Info Centre, Alberta Agriculture and Forestry.
 
 
 
 
Share via AddThis.com
For more information about the content of this document, contact the Ag-Info Centre.
This information published to the web on May 31, 2004.
Last Reviewed/Revised on August 28, 2016.