About the Austin Daylily Rust Study?

The study began in the fall of 2020. The plan is to continue the study for several years. Gradually branching out to other rust prone regions of the country.

The Objectives

The main objective is to identify and 'score' highly rust resistant cultivars that are not in previous studies. The second objective is to generate additional scores for daylilies in the Daylily Rust.org study. There are a lot that don't have enough observations to report a score (a minimum of 3 is required). The final objective is to identify cultivars that appear to be immune to daylily rust.

The Methodology

This study’s methodology consists of making what are called 'observations' of individual clumps of registered cultivars. At least two observations will be made of a clump each year. The gardens participating in the study will not have sprayed fungicide for rust during the year the observations are made in a garden. For a clump to be included in the study the cultivars name MUST be accurately identified. If there is any doubt about the cultivars name, the clump will not be included in that gardens set of observations.

The Austin Trial

In 2022 the decision was made to have 4 beds dedicated to trialing cultivars for their rust resistance. More information about the Austin Trial can be found by clicking here.

About 2022

Central Texas had 2 hard freezes with temperatures around 20 degrees. Most evergreen daylilies had their folage frozen nearly to the ground. Austin had 58 100 degree days, the third worst in history. Rainfall was very scarce, central Texas has a deficit of 10 inches of rain for 2022. The high heat and lack of rainfall kept rust subdued until late fall. It took until August for rust to spread, we had 5 inches of rain over 2 weeks. By November rust was spreading again as we had some rain and very high humidity. The most susceptible cultivars had rust as bad as previous years. Most other cultivars had somewhat lower rust scores than previous years.

Some more detailed information about 2022 can be found here. A word document summary with ranked scores of the daylilies studied in 2022 can be downloaded from here.

About 2021

In February of 2021 Texas was hit with the most extreme cold weather in the last 30 years. For the first time since daylily rust became a problem it disappeared from most gardens around Austin. Gardens that overwintered daylilies in pots and protected them or brought plants in in the spring, quickly had rust reappear. By the fall there was sufficient rust to evaluate daylilies in 5 of the 8 gardens planned to be in the 2021 study. The 3 gardens with little or no rust had not added daylilies until the fall, and had not protected potted daylilies. We did find some rust on some of the fall added daylilies.

Some more detailed information about 2021 can be found here. A word document summary with ranked scores of the daylilies studied in 2021 can be downloaded from here.

How to arrange daylilies for a rust study

In order to sucessfully determine a cultivars rust resistance, there needs to be substantial rust around it. Plant trial daylilies to study next to very susceptible daylilies. An ideal layout would have a susceptible daylily in every other location in a row, with trial plants in between. This layout provides rust on at least 2 sides of the trial daylilies. Keep a few susceptible daylilies in pots, that are overwintered in a frost free location. As soon as the weather warms, place these pots next to susceptible daylilies to ensure they get reinfected early in the spring. You will have a pretty good idea as to how resistant your trial cultivars are after the first year. If the trial daylily is very susceptible this layout will quickly reveal that.

When to take an observation

Wait to begin taking observations until rust is very bad on rust prone plants. Ideally rust prone plants should be in the vicinity of plants you wish to take observations of. If you have seen rust on the cultivar you are interested in observing in the past, but see none now, wait until you see rust on the plant that approximates or is worse than what you have seen in the past. Once temperatures get into the high 90’s, you should suspend taking observations until temperatures moderate in the fall, and rust begins actively spreading again.

Taking an observation

To take an observation the clump is examined for a leaf containing the most rust, a leaf with rust on both the upper/top and underside/bottom is the one to choose. That leaf is detached close to the crown.

Daylily leafs are long and thin. The length measurements refer to the long dimension. When taking the top and bottom of the leafs length of rust, if rust only appears on 2 inches in the long direction then record 2. This measurement does not need to be perfect. We are simply trying to get an approximate percentage of the long dimension of the leaf with rust on it. The cobb scale measurements will capture the density of the rust on the leaf.

A set of five measurements are made of the leaf:

1 The length of the leaf
2 The length of visible rust on the bottom/under-side of the leaf.
3 The length of visible rust on the top/upper-side of the leaf.
A Daylily Rust modified cobb scale graphic is held beside the leaf and the closest graphic that matches the density of rust on the leaf is chosen. One of the cobb scales is shown here.
4 A cobb scale reading of the bottom/under-side of the leaf is taken.
5 A cobb scale reading of the top/upper-side of the leaf is taken.

The five measurements, along with the cultivars name are entered into an excel spreadsheet. The spreadsheet has extensive validation checking on the data being entered. As far as the observer is concerned the clumps observation is finished.

The Calculation of the observations score performed by the spreadsheet or a computer program

The observation is reduced to 4 values that go into the database.

Percent linear rust on leaf bottom: linbotplc = measurement 2 ÷ measurement 1.
Percent linear rust on leaf top: lintopplc = measurement 3 ÷ measurement 1
Cobb scale density bottom: bc = measurement 4
Cobb scale density top: tc = measurement 5
The bottom of the leaf's % rust coverage: bot% = linbotplc x bc
The top of the leaf's % rust coverage: top% = lintopplc x tc

If the top% is greater than 4%, 6.25% is added to bot%. This has the effect of either pushing the score out of the range it is in or at least pushing it to the top of the range.

The observations score is equal to (bot% / 12.5%), calculated to 2 decimal places. If the score is > 0, 1 is added. If the score is > 5, the score is capped at 5.0. The score will now be in one of the studies 6 ranges, 0,1.0-1.99,2.0-2.99,3.0-3.99,4.0-4.99,5.0.