I think the rose developed rose canker. I have had several roses with this problem. The solution is to prune back to where you see only green canes and then treat with lime and sulfur solution. That has worked for me-it is sold at Ace Hardware store or Home Depot. Make sure you sterilize the pruner after use.
Pitting resistance equivalent number (PREN) is a measurement of the corrosion resistance of various types of stainless steel.Exact testing procedures are specified in the ASTM G48 standard. In general: the higher PREN-value, the more corrosion resistant the steel.The PREN-value is calculated using the following formula: PREN = 1 x %Cr + 3.3 x %Mo + 16 x %N (w/w) Steels with PREN-values above 32 are considered seawater (corrosion) resistant.urthermore a PREN-value â¥ 40 for duplex steels is called for in the DIN EN ISO 15156 as well as the American NACE â a standard for use in hydrogen sulfide environments known in the oil and gas extraction industries. Exception: stainless steels with molybdenum content â¥ 1.5% may have a PREN-value â¥ 30.
With regards to pitting, the PREN table is usually quite valid. Stress Corrosion Cracking (âStainless Steel and Corrosionâ, Chapter 6.4) Stress corrosion cracking (SCC, Spannungsrisskorrosion, spannungsriÃkorrosion) spaendingskorrosion spÃ¦ndingskorrosion is a type of-corrosion gi ving rise. to crackswo steel grades with the same PREN can therefore be expected to perform equally good towards pitting corrosion.PREN = %Cr + 3,3 â¢ %Mo + 16 â¢ %NPlease note that molybdenum (Mo) works with a factor 3.3 and is therefore 3.3 times better than a si-milar amount of chromium (Cr).